Haematological effects of radioimmunotherapy in cancer patients

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Abstract
Summary. The haematologic effects of radioimmunotherapy (RAIT) in cancer patients have been studied in order to better understand the aetiology of RAIT‐associated myelosuppresion. Evaluations were performed on patients treated with 131I‐anti‐carcinoembryonic antigen (CEA) and 131I‐LL2, a monoclonal antibody (MAb) reactive with non‐Hodgkin's B‐cell lymphoma. Both groups of patients experienced decreases in WBC and platelets. Nadirs were observed 42–51 d post first injection in the lymphoma patients, and 49–66 d post first injection (30–43 d post high‐dose therapeutic injection) in the carcinoma patients. Within the WBC population, B cells were the most radiosensitive. The evaluations of the binding of these MAbs to peripheral blood cells and the effect of RAIT on lymphocyte subpopulations indicated a drop of 26–92% in the percentage of B lymphocytes within 1 week following treatment with both 131I‐LL2 and 131I‐anti‐CEA MAbs even though only LL2 binds to B cells. The percentage of T lymphocytes was not affected by the 131I‐antibody treatments.These observations suggest that the marked drop in circulating B lymphocytes and platelets after the administration of radioiodinated antibodies is a nonspecific radiation effect, and not necessarily related to the binding of MAb to normal B cells. Thus, among WBCs, B cells are uniquely radiosensitive, and will be unusually affected by antibody‐directed internal radiation.