A distinctive pattern of serial immunologic determinations was observed in a patient during tumor remission on 5-fluorouracil therapy when compared with patterns observed among 7 other patients not having remission on either cytotoxic or endocrine therapy. This pattern was characterized by a transient decline in T (thymus-derived) lymphocyte levels with a rebound to above normal levels during the height of the remission and a subsequent fall in T cell levels some weeks before relapse was detected clinically. Serum IgG (immunoglobulin G) levels declined during treatment, while serum IgA (immunoglobulin A) and IgM (immunoglobulin M) levels increased. The results suggest that a drug-induced reduction in tumor burden may result in an increase in the number and activity of T lymphocytes in the peripheral circulation, while relapse on therapy may be associated with a fall in T lymphocyte levels. These findings indicate that the effects of antiproliferative agents on the host-tumor relationship may provide important insights into the biologic nature of cancer.
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