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)

Subjects were randomized to receive either tositumomab (Anti-B1 Antibody) and iodine I 131 tositumomab (Arm A) or unlabeled tositumomab (Arm B). Subjects randomized to Arm B were allowed to cross over and receive I 131 tositumomab once their disease had progressed as long as they still fulfilled the protocol entry criteria (except for exclusion criterion 12, prior monoclonal antibody therapy) and were human anti-murine antibody (HAMA) negative. Study endpoint assessments of response were conducted by a Masked Independent Randomized Radiographic and Oncologic Review (MIRROR) panel and the Study Investigators' assessments of safety and survival. Subjects who completed at least two years of follow-up in Protocol BEX104515 (formerly Corixa Protocol RIT-II-002) were enrolled in long term follow-up Protocol BEX104526 (formerly Corixa Protocol CCBX001-051), an administrative protocol, for continued radiographic response evaluations and safety evaluations every 6 months for years 3 through 5 post-treatment and annually for years 6 through 10 post-treatment. Subjects in BEX104526 were assessed for survival, disease status, subsequent therapy for NHL, and long-term safety, including the use of thyroid medication, development of hypothyroidism, human anti murine antibody (HAMA), myelodysplastic syndrome, acute myelogenous leukemia, and all other secondary malignancies. Additionally, subjects were followed for the development of any adverse event(s) deemed by the Principal Investigator as being possibly or probably related to a subject's previous treatment with Iodine I-131 tositumomab. Laboratory evaluations consisting of a thyroid stimulating hormone level and a complete blood cell count, with a differential and platelet count, were obtained annually through year 10 post-treatment.

Dosimetric Dose: Subjects received 450 mg of tositumomab IV followed by 5.0 mCi of Iodine I-131 and 35 mg of tositumomab. Following the dosimetric dose, whole body dosimetry was performed on each subject using a total body gamma camera. Whole body anterior and posterior whole body images were obtained at the following timepoints.

1. Within one hour of infusion of the dosimetric dose and prior to urination
2. 2-4 days after infusion of the dosimetric dose, following urination
3. 6-7 days after infusion of the dosimetric dose, following urination Therapeutic Dose: The total body residence time, derived from total body gamma camera counts obtained at the 3 time points, was used to calculate the iodine-131 activity (mCi) to be administered to deliver the therapeutic total body irradiation dose of 65 or 75 cGy. The therapeutic step was administered 7-14 days after the dosimetric step and consisted of tositumomab 450 mg followed by an activity (mCi) of iodine-131 calculated to deliver 75 cGy or 65 cGy of total body irradiation, depending on platelet count, and 35 mg of tositumomab.

For subjects with ≥150,000 platelets/mm3, the recommended dose was the activity of iodine-131 calculated to deliver 75 cGy of total body irradiation; for subjects with NCI Grade 1 thrombocytopenia (platelet counts ≥100,000 but \<150,000 platelets/mm3), the recommended dose was the activity of iodine-131 calculated to deliver 65 cGy of total body irradiation.

This is a Phase II randomized, controlled, two-arm, open-label, multicenter study comparing the safety and efficacy of tositumomab and iodine I 131 tositumomab to tositumomab for the treatment of chemotherapy-relapsed or refractory low-grade or transformed low-grade B-cell NHL.

Treatment Arm A: Subject will undergo 2 phases of study. In the first phase, termed "dosimetric dose", subjects will receive tositumomab (450 mg) followed by tositumomab (35 mg) that has been trace labeled with 5mCi) Iodine-131 tositumomab. Whole body gamma camera scans will be obtained on day 0, day 2, 3, or 4, and day 6 or 7 following the dosimetric dose. Using the dosimetric data from three imaging time points, a subject-specific dose of iodine I 131 tositumomab to deliver the desired total body dose of radiotherapy will be calculated. In the second phase of the study, termed "therapeutic dose", subjects will receive unlabeled tositumomab (450mg) followed by iodine tositumomab (35mg) labeled with the subject-specific dose of iodine I-131 to deliver a whole body dose of 75 cGy to subjects. Subjects with platelet counts of 100,001 - 149,999 cells/mm3, will receive 65 cGy and subjects who are obese will be doses based on 137% of their lean body mass. Subjects will be treated with either saturated solution potassium iodide (SSKI), Lugol's solution, or potassium iodide tablets starting at least 24 hours prior to the first infusion of the Iodine-131 tositumomab (i.e., the dosimetric dose) and continuing for 14 days following the last infusion of radiolabeled tositumomab (i.e., the therapeutic dose).

Treatment Arm B: Subjects will receive the same amount of unlabeled tositumomab (450 + 35 mg) administered over the same time-frame as Arm A on the study Days 0 and 7 (the day 7 dose may be delayed but no longer than 14 days after the first dose).

Crossover treatment Arm B: Subjects in Arm B may crossover and receive Iodine-131 tositumomab following progression of their lymphoma if they still fulfill the protocol inclusion exclusion criteria (except exclusion criteria#12) and are HAMA-negative.

Eligibility Criteria:
Inclusion Criteria:

* Histologically confirmed low-grade or transformed NHL with evaluable, measurable disease
* Tumor had to express CD20 antigen
* One to three prior chemotherapy regimens
* Karnofsky performance score ≥60% and anticipated survival ≥3 months
* Absolute neutrophil count (ANC) \>1500/mm3 and platelet count \>100,000/mm3
* Adequate renal and hepatic function
* 18 years of age or older.
* Written informed consent and sign an IRB-approved Informed consent from prior to study entry.

Exclusion Criteria:

* More than an average of 25% of the intratrabecular marrow space involved by lymphoma in bone marrow biopsy specimens as assessed microscopically within 42 days of study entry. Bilateral posterior iliac crest core biopsies are required if the percentage of intratrabecular space involved exceeds 10% on a unilateral biopsy. The mean of bilateral biopsies must be no more than 25%.
* Received cytotoxic chemotherapy, radiation therapy, immunosuppressants, or cytokine treatment within FOUR weeks prior to study entry (6 weeks of nitrosourea compounds) or who exhibit persistent clinical evidence of toxicity. The use of steroids must be discontinued at least 1 week prior to study entry.
* Have undergone prior stem cell transplant.
* Active obstructive hydronephrosis.
* Evidence of active infection requiring intravenous antibiotics at the time of study entry.
* New York Heart Association class III or IV heart disease or other serious illness that would preclude evaluation.
* Prior malignancy other than lymphoma, except for adequately-treated skin cancer, in situ cervical cancer, or other cancer for which subject has been disease-free for 5 years.
* Known HIV infection.
* Known brain or leptomeningeal metastases.
* Pregnant or nursing. Subjects of childbearing potential must undergo pregnancy test within 7 days of study entry and antibody is not to be administered until a negative result is obtained. For those subjects in Arm B, the pregnancy test must be repeated within 7 days of crossover. Male and female must agree to use effective contraception for 6 months following the therapeutic dose, as applicable.
* Previous allergic reactions to iodine. This does not include reactions to intravenous iodine-containing contrast materials.
* Previously given any monoclonal or polyclonal antibodies of any non-human species for either diagnostic or therapeutic purpose. This includes engineered chimeric and humanized antibodies.
* Previously received radioimmunotherapy .
* Progressive disease within one year of irradiation arising in a field that has been previously irradiated with \>3500 cGy.
* de novo intermediate or high-grade lymphoma.
* Received \>3 chemotherapy regimens (different or identical agents).