Trial Outcomes & Findings for Safety and Efficacy of MK-1200 in Participants With Advanced Solid Tumors (MK-1200-002) (NCT NCT06242691)

Last Updated: 2026-06-05

Results Overview

The occurrence of any of the following toxicities within 28 days after the first dose of study intervention were considered a DLT, if assessed by the investigator to be possibly, probably, or definitely related to study intervention administration: * Grade 4 nonhematologic toxicity (not laboratory). Any nonhematologic AE ≥Grade 3 in severity was considered a DLT, with pre-specified exceptions * Any Grade 3 or Grade 4 laboratory value (hematologic or nonhematologic), with pre-specified exceptions * Febrile neutropenia Grade 3 or Grade 4 as prespecified by the protocol * Prolonged delay (\>2 weeks) in initiating Cycle 2 due to intervention-related toxicity * Any intervention-related toxicity that caused the participant to discontinue intervention during Cycle 1 * Missed \>25% of MK-1200 doses as a result of drug-related AEs during the first cycle * Grade 5 toxicity

Recruitment status

COMPLETED

Study phase

PHASE1/PHASE2

Target enrollment

13 participants

Primary outcome timeframe

During the first two 14-day cycles (Up to approximately 28 days)

Results posted on

2026-06-05

Participant Flow

In Part 1, a total of 13 participants received the following doses: 3.6 mg/kg (3 participants), 4.2 mg/kg (5 participants), and 4.8 mg/kg (5 participants). Part 2 was not initiated and no patients were enrolled.

Participant milestones

Participant milestones
Measure	Part 1: MK-1200 3.6 mg/kg In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 1: MK-1200 4.2 mg/kg In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.
Overall Study STARTED	3	5	5
Overall Study COMPLETED	0	0	0
Overall Study NOT COMPLETED	3	5	5

Reasons for withdrawal

Reasons for withdrawal
Measure	Part 1: MK-1200 3.6 mg/kg In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 1: MK-1200 4.2 mg/kg In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.
Overall Study Death	2	5	4
Overall Study Sponsor Decision	1	0	0
Overall Study Withdrawal by Subject	0	0	1

Baseline Characteristics

Safety and Efficacy of MK-1200 in Participants With Advanced Solid Tumors (MK-1200-002)

Baseline characteristics by cohort

Baseline characteristics by cohort
Measure	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Total n=13 Participants Total of all reporting groups
Age, Continuous	63.7 Years STANDARD_DEVIATION 13.6 • n=20 Participants	64.0 Years STANDARD_DEVIATION 8.7 • n=20 Participants	62.0 Years STANDARD_DEVIATION 8.3 • n=40 Participants	—	—	63.2 Years STANDARD_DEVIATION 8.9 • n=13 Participants
Sex: Female, Male Female	1 Participants n=20 Participants	5 Participants n=20 Participants	0 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	6 Participants n=13 Participants
Sex: Female, Male Male	2 Participants n=20 Participants	0 Participants n=20 Participants	5 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	7 Participants n=13 Participants
Ethnicity (NIH/OMB) Hispanic or Latino	0 Participants n=20 Participants	1 Participants n=20 Participants	1 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	2 Participants n=13 Participants
Ethnicity (NIH/OMB) Not Hispanic or Latino	3 Participants n=20 Participants	4 Participants n=20 Participants	4 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	11 Participants n=13 Participants
Ethnicity (NIH/OMB) Unknown or Not Reported	0 Participants n=20 Participants	0 Participants n=20 Participants	0 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	0 Participants n=13 Participants
Race (NIH/OMB) American Indian or Alaska Native	0 Participants n=20 Participants	0 Participants n=20 Participants	0 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	0 Participants n=13 Participants
Race (NIH/OMB) Asian	0 Participants n=20 Participants	0 Participants n=20 Participants	0 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	0 Participants n=13 Participants
Race (NIH/OMB) Native Hawaiian or Other Pacific Islander	0 Participants n=20 Participants	0 Participants n=20 Participants	0 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	0 Participants n=13 Participants
Race (NIH/OMB) Black or African American	0 Participants n=20 Participants	0 Participants n=20 Participants	0 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	0 Participants n=13 Participants
Race (NIH/OMB) White	3 Participants n=20 Participants	5 Participants n=20 Participants	5 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	13 Participants n=13 Participants
Race (NIH/OMB) More than one race	0 Participants n=20 Participants	0 Participants n=20 Participants	0 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	0 Participants n=13 Participants
Race (NIH/OMB) Unknown or Not Reported	0 Participants n=20 Participants	0 Participants n=20 Participants	0 Participants n=40 Participants	0 Participants n=6 Participants	0 Participants n=7 Participants	0 Participants n=13 Participants

PRIMARY outcome

Timeframe: During the first two 14-day cycles (Up to approximately 28 days)

Population: All randomized participants in Part 1 who received at least one dose of study intervention and met the criteria for DLT evaluability (participants in Part 1 who completed Cycle 1 without a DLT or experienced a DLT during Cycle 1). One participant withdrew consent during the DLT evaluation period and was excluded from DLT analysis.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=4 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
Number of Participants Who Experience One or More Dose-Limiting Toxicities (DLTs) - Part 1	0 Participants	1 Participants	0 Participants	—	—

PRIMARY outcome

Timeframe: Up to approximately 12 months

Population: All randomized participants in Part 1 and Part 2 who received at least one dose of study intervention. No participants were enrolled in Part 2; thus, no data were collected or analyzed for Part 2.

An AE was any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. The number of participants who experienced an AE is reported for each arm.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
Number of Participants Who Experience One or More Adverse Events (AEs) - Part 1 & Part 2	5 Participants	5 Participants	3 Participants	—	—

PRIMARY outcome

Timeframe: Up to approximately 9 months

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
Number of Participants Who Discontinue Study Intervention Due to an AE - Part 1 & Part 2	0 Participants	0 Participants	0 Participants	—	—

SECONDARY outcome

Timeframe: Up to approximately 13 months

Population: As pre-specified by the protocol, this analysis was to only include all participants randomized to Part 2 Cohort A who received at least 1 dose of study intervention. No participants enrolled in Part 2; thus, no data were collected or analyzed.

ORR was defined as the percentage of participants who have achieved confirmed Complete Response (CR: disappearance of all target lesions) or a Partial Response (PR: at least a 30% decrease in the sum of diameters of target lesions) per RECIST 1.1 as assessed by blinded independent central review (BICR). As pre-specified by the protocol, this analysis was to only include all participants randomized to Part 2 Cohort A who received at least 1 dose of study intervention.

Outcome measures

Outcome data not reported

SECONDARY outcome

Timeframe: Up to approximately 13 months

Population: All randomized participants in Part 1 and Part 2 Cohort B who received at least one dose of study intervention. No participants were enrolled in Part 2; thus, no data were collected or analyzed for Part 2.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
ORR Per RECIST 1.1 as Assessed by Investigator - Part 1 & Part 2 Cohort B	0 Percentage of Participants Interval 0.0 to 52.2	0 Percentage of Participants Interval 0.0 to 52.2	0 Percentage of Participants Interval 0.0 to 70.8	—	—

SECONDARY outcome

Timeframe: Cycle 1 Day 1: predose and 0.5, 2, 4, 8, 24, 72, 168, 240, and 336 hours postdose. A cycle was 14 days.

Population: The subset of participants in Part 1 and Part 2 who complied with the protocol and had available data from at least one treatment administration were to be analyzed. No participants were enrolled in Part 2; thus, no data were collected or analyzed for Part 2.

AUC0-336 was defined as the area under the concentration versus time curve of MK-1200-ADC from time 0 to 336 Hours. Blood samples were collected at pre-specified timepoints to determine the AUC0-336 of the MK-1200-ADC.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
Area Under the Concentration Versus Time Curve From Time 0 to 336 Hours (AUC0-336) of MK-1200-Antibody-Drug Conjugate (ADC) - Parts 1 and 2	4310 hr*μg/mL Geometric Coefficient of Variation 40.9	3770 hr*μg/mL Geometric Coefficient of Variation 24.5	2840 hr*μg/mL Geometric Coefficient of Variation 49.7	—	—

SECONDARY outcome

Timeframe: Cycle 1 Day 1: predose and 0.5, 2, 4, 8, 24, 72, 168, 240, and 336 hours postdose. A cycle was 14 days.

AUC0-336 was defined as the area under the concentration versus time curve of KL610023 from time 0 to 336 Hours. Blood samples were collected at pre-specified timepoints to determine AUC0-336 of KL610023.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
AUC0-336 of the Conjugated Toxin Payload (KL610023) - Parts 1 and 2	748 hr*ng/mL Geometric Coefficient of Variation 18.9	583 hr*ng/mL Geometric Coefficient of Variation 173.9	329 hr*ng/mL Geometric Coefficient of Variation 40.8	—	—

SECONDARY outcome

Timeframe: Cycle 4 Day 1: predose and 0.5, 2, 4, 8, 24, 72, 168, 240, and 336 hours postdose. A cycle was 14 days.

AUC0-tau was defined as the area under the concentration versus time curve of MK-1200-ADC from time 0 to the end of the 14-day dosing period (Cycle 4, 336 hours post-dose). Blood samples were collected at pre-specified timepoints to determine AUC0-tau of the MK-1200-ADC.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=4 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=1 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
Area Under the Concentration Versus Time Curve From Time 0 to the End of the Dosing Period (AUC0-tau) of MK-1200-ADC - Parts 1 and 2	4070 hr*μg/mL Geometric Coefficient of Variation 35.8	2580 hr*μg/mL Geometric Coefficient of Variation NA NA = Percent geometric coefficient of variation was not calculated when N \< 2.	3130 hr*μg/mL Geometric Coefficient of Variation 40.3	—	—

SECONDARY outcome

Timeframe: Cycle 4 Day 1: predose and 0.5, 2, 4, 8, 24, 72, 168, 240, and 336 hours postdose. A cycle was 14 days.

AUC0-tau is defined as the area under the concentration versus time curve of KL610023 from time 0 to the end of the 14-day dosing period (Cycle 4, 336 hours post-dose). Blood samples were collected at pre-specified timepoints to determine AUC0-tau of KL610023.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=4 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=1 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
AUC0-tau of KL610023 - Parts 1 and 2	723 hr*ng/mL Geometric Coefficient of Variation 19.9	308 hr*ng/mL Geometric Coefficient of Variation NA NA = Percent geometric coefficient of variation was not calculated when N \< 2.	319 hr*ng/mL Geometric Coefficient of Variation 25.9	—	—

SECONDARY outcome

Timeframe: Day 1 of Cycles 1 and 4: predose and 0.5, 2, 4, 8, 24, 72, 168, 240, and 336 hours postdose. A cycle was 14 days.

Cmin was defined as the minimum concentration of MK-1200-ADC observed in plasma after its administration and just prior to administration of a subsequent dose. Blood samples were collected at pre-specified timepoints to determine Cmin of the MK-1200-ADC.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
Minimum Concentration (Cmin) of MK-1200-ADC - Part 1 & Part 2 Cycle 1 Day 1	NA μg/mL Geometric Coefficient of Variation NA NA = was not calculable due to Cmin values that were zero or below level of quantitation (BLOQ)	NA μg/mL Geometric Coefficient of Variation NA NA = was not calculable due to Cmin values that were zero or below level of quantitation (BLOQ)	0.176 μg/mL Geometric Coefficient of Variation 67.4	—	—
Minimum Concentration (Cmin) of MK-1200-ADC - Part 1 & Part 2 Cycle 4 Day 1	0.167 μg/mL Geometric Coefficient of Variation 64.7	0.390 μg/mL Geometric Coefficient of Variation NA NA = Percent geometric coefficient of variation was not calculated when N \< 2.	NA μg/mL Geometric Coefficient of Variation NA NA = was not calculable due to Cmin values that were zero or below level of quantitation (BLOQ)	—	—

SECONDARY outcome

Timeframe: Day 1 of Cycles 1 and 4: predose and 0.5, 2, 4, 8, 24, 72, 168, 240, and 336 hours postdose. A cycle was 14 days.

Cmin was defined as the minimum concentration of KL610023 observed in plasma after its administration and just prior to administration of a subsequent dose. Blood samples were collected at pre-specified timepoints to determine Cmin of KL610023.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
Cmin of KL610023 - Part 1 & Part 2 Cycle 4 Day 1	NA ng/mL Geometric Coefficient of Variation NA NA = was not calculable due to Cmin values that were zero or below level of quantitation (BLOQ)	NA ng/mL Geometric Coefficient of Variation NA NA = was not calculable due to Cmin values that were zero or below level of quantitation (BLOQ)	NA ng/mL Geometric Coefficient of Variation NA NA = was not calculable due to Cmin values that were zero or below level of quantitation (BLOQ)	—	—
Cmin of KL610023 - Part 1 & Part 2 Cycle 1 Day 1	NA ng/mL Geometric Coefficient of Variation NA NA = was not calculable due to Cmin values that were zero or below level of quantitation (BLOQ)	NA ng/mL Geometric Coefficient of Variation NA NA = was not calculable due to Cmin values that were zero or below level of quantitation (BLOQ)	NA ng/mL Geometric Coefficient of Variation NA NA = was not calculable due to Cmin values that were zero or below level of quantitation (BLOQ)	—	—

SECONDARY outcome

Timeframe: Day 1 of Cycles 1 and 4: predose and 0.5, 2, 4, 8, 24, 72, 168, 240, and 336 hours postdose. A cycle was 14 days.

Cmax was defined as the maximum or 'peak' concentration of MK-1200-ADC observed after its administration. Blood samples were collected at pre-specified timepoints to determine Cmax of the MK-1200-ADC.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
Maximum Concentration (Cmax) of MK-1200-ADC - Part 1 & Part 2 Cycle 1 Day 1	89.0 μg/mL Geometric Coefficient of Variation 42.9	73.7 μg/mL Geometric Coefficient of Variation 13.3	60.5 μg/mL Geometric Coefficient of Variation 34.2	—	—
Maximum Concentration (Cmax) of MK-1200-ADC - Part 1 & Part 2 Cycle 4 Day 1	84.7 μg/mL Geometric Coefficient of Variation 36.3	70.7 μg/mL Geometric Coefficient of Variation NA NA = Percent geometric coefficient of variation values were not calculated when N \< 2	68.1 μg/mL Geometric Coefficient of Variation 18.2	—	—

SECONDARY outcome

Timeframe: Day 1 of Cycles 1 and 4: predose and 0.5, 2, 4, 8, 24, 72, 168, 240, and 336 hours postdose. A cycle was 14 days.

Cmax was defined as the maximum or 'peak' concentration of KL610023 observed after its administration. Blood samples were collected at pre-specified timepoints to determine Cmax of KL610023.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
Cmax of KL610023 - Part 1 & Part 2 Cycle 1 Day 1	12.0 ng/mL Geometric Coefficient of Variation 21.6	15.8 ng/mL Geometric Coefficient of Variation 85.2	6.26 ng/mL Geometric Coefficient of Variation 49.4	—	—
Cmax of KL610023 - Part 1 & Part 2 Cycle 4 Day 1	15.5 ng/mL Geometric Coefficient of Variation 55.3	3.64 ng/mL Geometric Coefficient of Variation NA NA = Percent geometric coefficient of variation values were not calculated when N \< 2	6.50 ng/mL Geometric Coefficient of Variation 31.1	—	—

SECONDARY outcome

Timeframe: Up to approximately 13 months

Population: As pre-specified by the protocol, this analysis was to only include all participants randomized to Part 2 Cohort A who received at least 1 dose of study intervention and achieved CR or PR. No participants enrolled in Part 2; thus, no data were collected or analyzed.

For participants demonstrating a confirmed CR (disappearance of all target lesions) or PR (at least a 30% decrease in the sum of diameters of target lesions) per RECIST 1.1, DOR was defined as the time from the first documented evidence of a CR or a PR until Progressive Disease (PD) or death due to any cause, whichever occurred first. Per RECIST 1.1, PD was defined as ≥20% increase in the sum of diameters of target lesions. In addition to the relative increase of 20%, the sum must also have demonstrated an absolute increase of ≥5 mm. The appearance of one or more new lesions was also considered PD. As pre-specified by the protocol, DOR for Part 2 Cohort A was planned to be assessed by BICR and was to include all participants randomized to Part 2 Cohort A who received at least one dose of study intervention.

Outcome measures

Outcome data not reported

SECONDARY outcome

Timeframe: Up to approximately 13 months

Population: All randomized participants in Part 1 and Part 2 Cohort B who received at least one dose of study intervention and achieved CR or PR were analyzed. No participants were enrolled in Part 2; thus, no data were collected or analyzed for Part 2.

For participants demonstrating a confirmed CR (disappearance of all target lesions) or PR (at least a 30% decrease in the sum of diameters of target lesions) per RECIST 1.1, DOR is defined as the time from the first documented evidence of a CR or a PR until PD or death due to any cause, whichever occurs first. Per RECIST 1.1, PD is defined as ≥20% increase in the sum of diameters of target lesions. In addition to the relative increase of 20%, the sum must also demonstrate an absolute increase of ≥5 mm. The appearance of one or more new lesions is also considered PD. The DOR as assessed by the investigator is reported.

Outcome measures

Outcome data not reported

SECONDARY outcome

Timeframe: Up to approximately 13 months

PFS was defined as the time from randomization to the first documented PD by BICR or death due to any cause, whichever occurs first. Per RECIST 1.1, PD was defined as ≥20% increase in the sum of diameters of target lesions. In addition to the relative increase of 20%, the sum must also have demonstrated an absolute increase of ≥5 mm. The appearance of one or more new lesions was also considered PD. As pre-specified by the protocol, PFS for Part 2 Cohort A was planned to be assessed by BICR and was to only include all participants randomized to Part 2 Cohort A who received at least one dose of study intervention.

Outcome measures

Outcome data not reported

SECONDARY outcome

Timeframe: Up to approximately 13 months

PFS was defined as the time from randomization to the first documented PD by investigator or death due to any cause, whichever occurs first. Per RECIST 1.1, PD was defined as ≥20% increase in the sum of diameters of target lesions. In addition to the relative increase of 20%, the sum must also have demonstrated an absolute increase of ≥5 mm. The appearance of one or more new lesions was also considered PD. PFS as assessed by the investigator is reported.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
PFS Per RECIST 1.1 as Assessed by Investigator - Part 1 & Part 2 Cohort B	3.9 Months Interval 1.5 to NA= PFS range upper limit not reached	1.3 Months Interval 0.4 to NA= PFS range upper limit not reached	2.9 Months Interval 2.6 to NA= PFS range upper limit not reached	—	—

SECONDARY outcome

Timeframe: Up to approximately 13 months

OS was defined as the time from randomization to death due to any cause.

Outcome measures

Outcome measures
Measure	Part 1: MK-1200 4.2 mg/kg n=5 Participants In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 Participants In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 3.6 mg/kg n=3 Participants In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 2: MK-1200 Cohort A (Part 2-Not Enrolled) In Part 2, participants in Cohort A were to receive either Dose 1 or Dose 2 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.	Part 2: MK-1200 Cohort B (Part 2-Not Enrolled) In Part 2, participants in Cohort B were to receive Dose 1 of MK-1200 via IV infusion q2w until any discontinuation criteria were met. No participants were enrolled in this arm.
Overall Survival (OS) - Part 1 & Part 2	4.6 Months Interval 3.4 to NA= OS range upper limit not reached	3.7 Months Interval 1.6 to NA= OS range upper limit not reached	8.4 Months Interval 4.1 to NA= OS range upper limit not reached	—	—

Adverse Events

Part 1: MK-1200 3.6 mg/kg

Serious events: 1 serious events

Other events: 3 other events

Deaths: 2 deaths

Part 1: MK-1200 4.2 mg/kg

Serious events: 4 serious events

Other events: 5 other events

Deaths: 5 deaths

Part 1: MK-1200 4.8 mg/kg

Serious events: 0 serious events

Other events: 5 other events

Deaths: 4 deaths

Serious adverse events

Serious adverse events
Measure	Part 1: MK-1200 3.6 mg/kg n=3 participants at risk In Part 1, participants received 3.6 mg/kg of MK-1200 via IV infusion every 2 weeks (q2w) until any discontinuation criteria were met.	Part 1: MK-1200 4.2 mg/kg n=5 participants at risk In Part 1, participants received 4.2 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.	Part 1: MK-1200 4.8 mg/kg n=5 participants at risk In Part 1, participants received 4.8 mg/kg of MK-1200 via IV infusion q2w until any discontinuation criteria were met.
Gastrointestinal disorders Ascites	0.00% 0/3 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	20.0% 1/5 • Number of events 1 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	0.00% 0/5 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.
Gastrointestinal disorders Small intestinal obstruction	0.00% 0/3 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	40.0% 2/5 • Number of events 2 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	0.00% 0/5 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.
Hepatobiliary disorders Biliary obstruction	33.3% 1/3 • Number of events 1 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	0.00% 0/5 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	0.00% 0/5 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.
Infections and infestations Sepsis	0.00% 0/3 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	20.0% 1/5 • Number of events 1 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	0.00% 0/5 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.
Product Issues Device occlusion	33.3% 1/3 • Number of events 1 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	0.00% 0/5 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	0.00% 0/5 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.
Vascular disorders Embolism	0.00% 0/3 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	20.0% 1/5 • Number of events 1 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.	0.00% 0/5 • Up to approximately 13 months The population for all-cause mortality includes all allocated participants. The population for serious and nonserious AEs includes all participants in Part 1 and Part 2 who received at least one dose of study intervention and were analyzed according to treatment received. No participants were enrolled in Part 2; thus, no data were collected for Part 2.

Other adverse events

Additional Information

Senior Vice President, Global Clinical Development

Merck Sharp & Dohme LLC

Phone: 1-800-672-6372

Email: [email protected]

Results disclosure agreements

Principal investigator is a sponsor employee If publication activity is not directed by the Sponsor, the investigator agrees to submit all manuscripts or abstracts to the Sponsor before submission. This allows the Sponsor to protect proprietary information and to provide comments.
Publication restrictions are in place

Restriction type: OTHER