To determine the effects of chemotherapeutic regimens on the cellular immune mechanism, peripheral blood T lymphocyte levels were serially measured using the T rosette assay in 8 patients with metastatic prostatic cancer. Patients were randomly assigned to either 5 fluorouracil, cyclophosphamide or standard endocrine therapy. In all patients receiving cyclophosphamide T lymphocyte levels were reduced to approximately 25% of base line levels and remained low for the duration of therapy. By contrast the T lymphocyte pattern in patients receiving 5 FU was characterized by a transient 50% reduction lasting for approximately 6 wk, followed by a return toward base line levels. In 1 patient in whom an objective tumor remission was induced by 5 FU, the T lymphocyte counts rebounded to above normal levels and were sustained for most of the duration of the remission. Relapse was heralded by a return of T lymphocyte counts to subnormal levels. No significant alteration in T lymphocyte levels was observed in patients receiving standard endocrine therapy. The results suggest that reduction in tumor burdened by cytotoxic agents may mitigate tumor mediated immune suppression and thus result in rebound lymphocyte proliferation. However, persistent blockade of host defense mechanisms induced by chemotherapeutic agents may have a permissive effect on tumor growth.
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