Background: Several investigators have reported a considerable variability in the observed hematologic toxicity after radioimmunotherapy (RAIT) with monoclonal antibodies (MoAb) given at similar amounts of radioactivity based on body surface area and/or similar radiation absorbed doses given to the red marrow. The authors investigated various factors potentially affecting hematologic toxicity after RAIT with 131I-labeled anti-carcinoembryonic antigen (CEA) MoAb to identify the statistically significant factors from those commonly perceived clinically to substantially contribute to this toxicity.
Methods: Ninety-nine patients who received 131I-labeled anti-CEA MoAb for the treatment of CEA-producing cancers were assessed for platelet and white blood cell toxicity based on the common Radiation Therapy Oncology Group criteria. Multivariate regression analysis was used to identify the statistically significant factors affecting toxicity among the following variables: red marrow dose, baseline platelet and white blood cell counts, bone and/or marrow metastases, prior chemotherapy or radiotherapy, timing of prior chemotherapy or radiotherapy in relationship to RAIT, type and number of prior chemotherapeutic regimens, age, sex, antibody form, and cancer type.
Results and conclusions: Red marrow dose, baseline platelet or white blood cell counts, multiple bone and/or marrow metastases, and chemotherapy 3-6 months before RAIT were the only four significant factors affecting hematologic toxicity according to multivariate analysis. The identification of bone and/or marrow metastases and recent chemotherapy as significant factors for hematologic toxicity could be important in the design of future clinical trials.