Trial Outcomes & Findings for A Randomized Study of Iodine-131 Anti-b1 Antibody Versus Anti-b1 Antibody in Chemotherapy-relapsed/Refractory Low-grade or Transformed Low-grade Non-Hodgkin's Lymphoma (NHL) (NCT NCT01573000)

Participants (par.) received radioimmunotherapy of tositumomab (TST)/Iodine I 131 TST (Arm A) or unlabeled TST (Arm B) in 2 phases: dosimetric and therapeutic dose. Arm B par. were allowed to crossover and receive I 131 TST, if disease progressed. After TST treatment, par. could have entered a Long-Term Follow-Up study (BEX104526; NCT00240591).

A Randomized Study of Iodine-131 Anti-b1 Antibody Versus Anti-b1 Antibody in Chemotherapy-relapsed/Refractory Low-grade or Transformed Low-grade Non-Hodgkin's Lymphoma (NHL)

Responses had to be confirmed by 2 separate evaluations occurring \>=4 weeks apart. Par. with confirmed response include those with Complete Response (CR: complete resolution of all disease-related radiological abnormalities and the disappearance of all signs and symptoms related to the disease), Clinical Complete Response (CCR: complete resolution of all disease-related symptoms; residual foci, thought to be residual scar tissue, are present), or Partial Response (PR: \>=50% reduction in the sum of the products of the longest perpendicular diameters of all measurable lesions; no new lesions).

Participants receiving Unlabeled TST with progressive disease (defined as a \>=25% increase from the nadir value of the sum of the products of the longest perpendicular diameters of all measureable lesions or the appearance of any new lesion. Individual lesions must be \>2 centimeters \[cm\] in diameter by radiographic evaluation or \>1 cm in diameter by physical examination.) were assessed separately before and after receiving the crossover treatment of I 131 TST for confirmed response, which included participants with CR, CCR, and PR.

CR is defined as the complete resolution of all disease-related radiological abnormalities and the disappearance of all signs and symptoms related to the disease.

Responses had to be confirmed by 2 separate evaluations occurring \>=4 weeks apart. Par. with confirmed response include those with Complete Response (CR: complete resolution of all disease-related radiological abnormalities and the disappearance of all signs and symptoms related to the disease), Clinical Complete Response (CCR: complete resolution of all disease-related symptoms; residual foci, thought to be residual scar tissue, are present), or Partial Response (PR: \>=50% reduction in the sum of the products of the longest perpendicular diameters of all measurable lesions; no new lesions).

Participants receiving Unlabeled TST with progressive disease were assessed separately before and after receiving the crossover treatment of I 131 TST for CR. CR is defined as the complete resolution of all disease-related radiological abnormalities and the disappearance of all signs and symptoms related to the disease.

CCR is defined as the complete resolution of all disease-related symptoms; residual foci, thought to be residual scar tissue, are present. Generally, an unchanging lesion =\<2 cm in diameter by radiographic evaluation or =\<1 cm in diameter by physical examination can be considered scar tissue.

Participants receiving Unlabeled TST with progressive disease were assessed separately before and after receiving the crossover treatment of I 131 TST for CCR. CCR is defined as the complete resolution of all disease-related symptoms; residual foci, thought to be residual scar tissue, are present. Generally, an unchanging lesion =\<2 cm in diameter by radiographic evaluation or =\<1 cm in diameter by physical examination can be considered scar tissue.

CCR is defined as the complete resolution of all disease-related symptoms; residual foci, thought to be residual scar tissue, are present. Generally, an unchanging lesion =\<2 cm in diameter by radiographic evaluation or =\<1 cm in diameter by physical examination can be considered scar tissue. The extent of disease must be unchanged or decreased upon follow-up evaluations. If the extent of disease was unchanged or if further decreases occurred for 6 months or longer, the participant was reclassified as having a CR.

Participants receiving Unlabeled TST with progressive disease were assessed separately before and after receiving the crossover treatment of I 131 TST for CR + CCR.

Confirmed PR is defined as a \>=50% reduction in the sum of the products of the longest perpendicular diameters of all measurable lesions, with no new lesions.

Participants receiving Unlabeled TST with progressive disease were assessed separately before and after receiving the crossover treatment of I 131 TST confirmed PR. Confirmed PR is defined as a \>=50 percent reduction in the sum of the products of the longest perpendicular diameters of all measurable lesions, with no new lesions.

Responses had to be confirmed by 2 separate evaluations occurring \>=4 weeks apart. Par. with confirmed response include those with Complete Response (CR: complete resolution of all disease-related radiological abnormalities and the disappearance of all signs and symptoms related to the disease), Clinical Complete Response (CCR: complete resolution of all disease-related symptoms; residual foci, thought to be residual scar tissue, are present), or Partial Response (PR: \>=50% reduction in the sum of the products of the longest perpendicular diameters of all measurable lesions; no new lesions).

For all participants with CR, CCR, or PR, duration of response was defined as the time from first documented response to first documented progression. All confirmed responders included participants with CR, CCR, and PR, whereas confirmed complete responders included participants with CR and CCR.

Responses had to be confirmed by 2 separate evaluations occurring \>=4 weeks apart. Par. with confirmed response include those with Complete Response (CR: complete resolution of all disease-related radiological abnormalities and the disappearance of all signs and symptoms related to the disease), Clinical Complete Response (CCR: complete resolution of all disease-related symptoms; residual foci, thought to be residual scar tissue, are present), or Partial Response (PR: \>=50% reduction in the sum of the products of the longest perpendicular diameters of all measurable lesions; no new lesions).

Responses had to be confirmed by 2 separate evaluations occurring \>=4 weeks apart. Par. with confirmed response include those with Complete Response (CR: complete resolution of all disease-related radiological abnormalities and the disappearance of all signs and symptoms related to the disease), Clinical Complete Response (CCR: complete resolution of all disease-related symptoms; residual foci, thought to be residual scar tissue, are present), or Partial Response (PR: \>=50% reduction in the sum of the products of the longest perpendicular diameters of all measurable lesions; no new lesions).

Progression-free survival or time to progression is defined as the time from the dosimetric dose to the first documented occurrence of disease progression or death.

Progression-free survival or time to progression is defined as the time from the dosimetric dose to the first documented occurrence of disease progression or death.

Responses had to be confirmed by 2 separate evaluations occurring \>=4 weeks apart. Par. with confirmed response include those with Complete Response (CR: complete resolution of all disease-related radiological abnormalities and the disappearance of all signs and symptoms related to the disease), Clinical Complete Response (CCR: complete resolution of all disease-related symptoms; residual foci, thought to be residual scar tissue, are present), or Partial Response (PR: \>=50% reduction in the sum of the products of the longest perpendicular diameters of all measurable lesions; no new lesions).

Time from the date of enrollment (the date of randomization) to the first documented progression or death.

Overall survival is defined as the time from the treatment start date to the date of death by any cause.

An AE is any untoward medical occurrence in a participant administered a pharmaceutical product and which does not necessarily have a causal relationship with this treatment. Causality of AEs was determined by the investigators as "none," "remote," "possible," "probable," or "highly probable." AEs considered by the investigator as being at least remotely related to the study treatment were considered to be DR AEs. White blood cell (WBC) count and absolute neutrophil count (ANC) were measured as cells per millimeters cubed (mm\^3); hemoglobin was measured in grams per deciliter (g/dL).

An infection is the colonization of a host organism by a parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease. Specimen samples of the body fluid are cultured for testing whether the infectious organism is present and grown in the culture media to assess the growth pattern of the organisms present in the specimen. The culture results could be positive or negative. The positive culture results indicate that the tested participant has the infection under investigation, in which case therapeutic treatment with anti-infective is required.

Anti-infectives are capable of acting against infection, by inhibiting the spread of an infectious agent or by killing the infectious agent outright. Anti-infective is a general term that encompasses antibacterials, antibiotics, antifungals, antiprotozoans, and antivirals.

AEs were graded using the Common Toxicity Criteria from the Cancer Therapy Evaluation Program, Division of Cancer Therapy, National Cancer Institute. Grades: 0 = No adverse event or within normal limits; 1 = Mild adverse event; 2 = Moderate adverse event; 3 = Severe and undesirable adverse event; 4 = Life-threatening or disabling adverse event; 5 = Death related to adverse event.

AEs were graded using the Common Toxicity Criteria from the Cancer Therapy Evaluation Program, Division of Cancer Therapy, National Cancer Institute. Grades: 0 = No adverse event or within normal limits; 1 = Mild adverse event; 2 = Moderate adverse event; 3 = Severe and undesirable adverse event; 4 = Life-threatening or disabling adverse event; 5 = Death related to adverse event.

Participants were categorized according to their primary cause of death. Deaths due to progressive disease or to another reason ("Other") were not captured as serious adverse events (SAEs) and are thus not included in the SAE module.

Time to death from the last dose of study drug is the time from the last dose of study drug administered to the date of death. Deaths due to progressive disease or to another reason ("Other") were not captured as serious adverse events (SAEs) and are thus not included in the SAE module.

An SAE is any event occurring at any dose that results in any of the following: death, a life-threatening adverse drug experience (ADE; at immediate risk of death from the experience as it occurred), inpatient hospitalization/prolongation of existing hospitalization, a persistent/significant disability/incapacity, or a congenital anomaly/birth defect. Medical events that may not result in death, be life-threatening, or require hospitalization may be considered to be a serious ADEs when based upon appropriate medical judgment. Relatedness was based on the investigator's medical judgement.

An SAE is any event occurring at any dose that results in any of the following: death, a life-threatening adverse drug experience (ADE; at immediate risk of death from the experience as it occurred), inpatient hospitalization/prolongation of existing hospitalization, a persistent/significant disability/incapacity, or a congenital anomaly/birth defect. Medical events that may not result in death, be life-threatening, or require hospitalization may be considered to be a serious ADEs when based upon appropriate medical judgment. Relatedness was based on the investigator's medical judgement.

Nadir is defined as the lowest laboratory value recorded following the administration of the study medication. Time to recovery to baseline in hematologic laboratory evaluations is the time required for recovery from nadir values to baseline values. Hematologic laboratory evaluations included ANC, hemoglobin (Hb), platelets (Plt), and WBC count.

Nadir is defined as the lowest laboratory value recorded following the administration of study medication. ANC is a measure of the number of neutrophil granulocytes present in the blood. Neutrophils are a type of white blood cell that fights against infection.

Nadir is defined as the lowest laboratory value recorded following the administration of study medication. Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells.

Nadir is defined as the lowest laboratory value recorded following the administration of study medication. Platelets and WBCs are types of blood cells.

Adverse events were graded using the Common Toxicity Criteria from the Cancer Therapy Evaluation Program, Division of Cancer Therapy, National Cancer Institute. Grades: 0 = No adverse event or within normal limits; 1 = Mild adverse event; 2 = Moderate adverse event; 3 = Severe and undesirable adverse event; 4 = Life-threatening or disabling adverse event; 5 = Death related to adverse event.

Adverse events were graded using the Common Toxicity Criteria from the Cancer Therapy Evaluation Program, Division of Cancer Therapy, National Cancer Institute. Grades: 0 = No adverse event or within normal limits; 1 = Mild adverse event; 2 = Moderate adverse event; 3 = Severe and undesirable adverse event; 4 = Life-threatening or disabling adverse event; 5 = Death related to adverse event.

Tositumomab is a murine (mouse) antibody (immunoglobulin) of the IgG2a subclass. Participants in this study were evaluated to determine whether they developed an immune response to study treatment as evident by human anti-mouse antibodies (HAMA) after administration of tositumomab and iodine I 131 tositumomab. A positive HAMA value indicates that the participant developed human anti-mouse antibodies above the HAMA assay threshold, and a negative HAMA value indicates either the absence or below threshold level of human anti-mouse antibodies.