Changes in Cellularity Induced by Radiation in a Solid Tumour

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Abstract
The growth and cellular responses of Morris rat hepatoma 3924 A to a locally administered dose of 3750 R X-rays were studied using relative tumor volume changes; 3H-thymidine (3H-TdR) incorporation into DNA; tumor DNA content and cellular analysis, including 3H-TdR labeling index, mitotic index, aberrant mitotic frequency and relative cell density. Before depression of tumor growth, cell proliferation is temporarily interrupted. As proliferation is reinitiated, a short-lived synchrony and prolongation of cell cycle tranverse are reflected in the labeling index and mitotic index, the relative cell density and the rate of incorporation of H-TdR into DNA. Within 4 days after radiation, cell proliferation and 3H-TdR incorporation are significantly depressed. Simultaneously there are reductions in the relative cell density and tumor DNA contents, and these remain depressed as the tumors initiate regression. It is apparent that the cellular responses to radiation insult occur in advance of measurable volume changes and are observed in tumors that continue to regress and those that initiate regrowth.