FDA Presentation to the Oncologic Drugs Advisory Committee Tositumomab Therapeutic Regimen Corixa Corporation BLA December 17, 2002

Tositumomab Therapeutic Regimen Review Team Product/Chairperson:Terrye G. Zaremba, Ph.D. Clinical Reviewers:Stephen Litwin, M.D. George Mills, M.D. Harvey Luksenburg, M.D. Kaushikkumar Shastri, M.D. Biostatistician:Satish Misra, Ph.D. Pharm/Tox:Martin D. Green, Ph.D. Radiochemistry:Leon Epps, Ph.D. BioResearch Monitor:Mary Andrich, M.D. Facilities Specialist:Deborah Trout, B.S. Project Managers:Karen Jones, B.S. Craig Doty, Pharm. D Michael A. Noska, M.S

Submission Time-Line Sept 14, BLA submitted –RIT-II /31/2000 study report –RIT-II-000 and 001- final study reports –RIT-II-002 and 003-interim study reports –ISS subjects Dec 14, 2000 –CP interim study report –ISS subjects

Timeline (2) March 16, 2001 – FDA Action letter #1 –Multiple requests for info on product characterization and manufacture –Inadequate efficacy database -single pivotal trial with substantially different efficacy in transformed vs. non-transformed, some supportive data submitted as interim reports –Inadequate safety database - substantial missing data for acute heme toxicity and delayed hematologic, thyroid and HAMA events

Timeline (3) August 27, 2001 –RIT-II-003 second interim report through 12/20/2000 –ISS update – 309 patients Sept 7, 2001 –Final study report CP –Amended study report RIT-II MIRROR panel review, data cut-off Jan. 2001

Timeline (4) Sept 10, Corixa response to FDA letter Dec 11, 2001 –RIT-II-004- amended final study report, data cutoff Jan 2001, MIRROR panel review Sept 2001 –ISS update – 620 patients (includes 387 from expanded access) –Long-term responders- various studies- MIRROR panel review –Additional info for CP98-020

Timeline (5) March 5, 2002 –ISS update: corrected errors & gave additional hematology data collected from audit at clinical study sites in 620 pts March 12, FDA action letter #2 –Need to demonstrate a meaningful therapeutic advance over existing treatment (Zevalin approved Feb. 2002) –Additional safety data needed

Timeline (6) July 2, 2002 –Case report forms and report tabulations for long-term responder subpopulation July 11, 2002 –Revised proposed indication –Requested accelerated approval for chemo-refractory and standard approval for Rituximab-refractory pts –Amendment 1 to final study report for CP97-012

Timeline (7) October 4, 2002 –Amendment 2 to final study report for CP October 30, 2002 –Independent review for additional patients with transformed histology in CP October 31, 2002 – Corixa completes response to FDA 3/12/2002 letter

Timeline (8) December 10, 2002 –Responses to Bi Mo inspectional findings Outstanding issues on clinical trial –identification of dose delivered vs. dose prescribed for patients in efficacy studies –FDA will need to confirm safety profile of proposed dose

Tositumomab Therapeutic Regimen (TTR) Monoclonal Antibody Characteristics Tositumomab and I-131- Tositumomab Tositumomab also called “Anti-B1” Murine IgG 2a, l Recognizes CD20

Characteristics of CD20 Transmembrane phosphoprotein with a molecular weight of kDa Present on the surface of pre-B and mature B cells Expressed on >90% of B-cell lymphomas Not present on stem cells, mature plasma cells, or other nonlymphoid normal tissues Is not shed or internalized upon antibody binding

Monoclonal Antibody Characteristics (2) Manufactured by standard tissue culture and purification techniquees I-131- Tositumomab radiolabeled by the IODO-GEN® method

TTR Components Unlabeled: -Tositumomab 3 mL vial: mg/mL -Tositumomab 20 mL vial: mg/mL

TTR Components (2) Labeleld (I-131-Tositumomab –Dosimetric vial: not less than 20 mL in a 30 mL vial. Protein concentration between 0.10 and 0.25 mg/mL. Calibrated activity of mCi. –Therapeutic vial: not less than 20 mL in a 30 mL vial. Protein concentration between 1.1 and 2.5 mg/mL. Calibrated activity of

TTR Procedure Step 1 – Imaging Tositumomab 450 mg in 0.9% NaCl injection in total volume of 50 mL IV over 60 minutes I-131 Tositumomab (dosimetric) 5 mCi + 35 mg Tositumomab in 0.9% NaCl injection in total volume of 30 mL IV over 20 minutes

TTR Procedure Step 2 - Therapy (7-14 days post imaging) Tositumomab 450 mg in 0.9% NaCl injection in total volume of 50 mL IV over 60 minutes I-131-Tositumomab (therapeutic) 35 mg containing the patient-specific dose (mCi) IV over 20 minutes

TTR Procedure Thyroid protective agent is given beginning at least 24 hours prior to the first infusion of I-131 Tositumomab (dosimetric dose) and continues for 14 days following the last infusion of I-131 Tositumomab (therapeutic dose).

Remaining CMC Issues A number of manufacturing issues remain to be resolved One contract facility remains to be inspected