Quantitation of cell shedding into efferent blood of mammary adenocarcinoma

The rate of tumor cell shedding into efferent tumor blood was measured in growing and regressing MTW9 rat mammary carcinomas. The hormone-dependent tumor, grown as an 'isoession was induced by reduction of mammotropin level in the host. Tumor cells were differentiated from normal leukocytes by indirect immunofluorescence. Growing tumors shed 3.2 x 10-6 and regressing tumors shed 4.1 x 10-6 cells per 24 hr per g tissue. Cell shedding rates of growing versus regressing tumors were not siginificantly different over a tumor size range of 2 to 4 g. The number of tumor cells in the arterial blood was 12-fold smaller than in the efferent tumor blood. It is concluded that: (ay cell shedding via blod probably plays only a minor role in the total cell loss by gtowing MTW9 carinomas; (b) hormone-induced tumor regression does not depend on increased cell shedding; (c) tumor cells are rapidly cleared from circulating blood; and (d) a 2-g MTW9 carcinoma pours enough cells into the host circulation to transplant the tumor every 24 hr.