Pivotal Study of Iodine I 131 Tositumomab for Chemotherapy-refractory Low-grade or Transformed Low-grade B-cell Non-Hodgkin's Lymphoma

Participants with response include those with CR, CCR, or PR. Criteria for CR: complete resolution of all disease-related radiological abnormalities and the disappearance of all signs and symptoms related to the disease. Criteria for CCR: complete resolution of all disease-related symptoms, but residual foci, thought to be residual scar tissue, are present. Criteria for PR: >=50% 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 CR, CCR , or PR. A confirmed response (CR/CCR/PR) had to be confirmed by a consecutive response (>=28 days [ 4 weeks] later) that was the same or better. Individual confirmed response data only counts that response confirmed by the same response; thus, not all possible combinations are represented.

Time to progression or progression-free survival is defined as the time from the dosimetric dose to the first documented occurrence of disease progression or death. Disease progression is defined as a >=25% increase from the nadir value (lowest laboratory value recorded following administration of the study medication) of the sum of the products of the longest perpendicular diameters of all measurable lesions or the appearance of any new lesion. Individual lesions must be >2 cm in diameter by radiographic evaluation or >1 cm in diameter by physical examination.

Time to treatment failure is defined as the length of time from the date of enrollment to the first incidence of treatment withdrawal, study removal, progression, and/or alternative therapy for the participant's lymphoma, or death.

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

Participants with response include those with CR, CCR, or PR. Criteria for CR: complete resolution of all disease-related radiological abnormalities and the disappearance of all signs and symptoms related to the disease. Criteria for CCR: complete resolution of all disease-related symptoms, but residual foci, thought to be residual scar tissue, are present. Criteria for PR: >=50% reduction in the sum of the products of the longest perpendicular diameters of all measurable lesions with no new lesions.

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. The Investigator assessed whether the adverse event was related to study drug.

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

AEs were graded using the Common Toxicity Criteria from the Cancer Therapy Evaluation Program, Division of Cancer Therapy, National Cancer Institute. Grades: 0 = No AE or within normal limits; 1 = Mild AE; 2 = Moderate AE; 3 = Severe and undesirable AE; 4 = Life-threatening or disabling AE; 5 = Death related to AE. The Investigator assessed whether the AE was possibly or probably related to study drug. In addition, all laboratory-derived hematologic toxicities (values outside the normal range) were assumed to be possibly or probably related to study drug.

The primary cause of death of the participants was assessed by the Investigator.

Time to death from the last dose of study drug is the time period difference between when study drug treatment stopped and when death occurred.

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 judgment.

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 AEs 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.

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.

The administration of murine antibodies may form HAMA. A HAMA assay was performed using the ImmunoSTRIP HAMA IgG enzyme-linked immune absorbent assay by a central laboratory (Covance Classic Laboratory Services, Indianapolis, IN). Fludarabine, a known immunosuppressant, might decrease HAMA production in addition to reducing bone marrow involvement. To be "positive," a participant had to have a positive HAMA assessment at any follow-up visit.

HAMA are human immunoglobulins with specificity for mouse immunoglobulins. HAMA assays were conducted in the laboratory to measure conversion to HAMA positivity following treatment. Time to HAMA positivity was calculated as the difference between the day on which HAMA positivity occurred and the first dosimetric dose administration day.

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. Grade 3/4 hematological toxicities: hemoglobin <8.0 g/dL; platelets <50,000 cells per millimeters (mm)^3; ANC <1000 cells per mm^3; WBC <2000 cells per mm^3.

Thyroid function was determined periodically, including during follow-up, in order to assess if there was any effect of the Iodine 131 on thyroid function. Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.