Enzyme activities in regressing estrone-induced mammary tumors of the rat.

Chemical and histochemical studies of three lysosomal enzymes-acid phosphatase, ß-glucuronidase, and cathepsinshowed that these enzymes increase during the regression of estrone-induced mammary tumors. One week after removal of the estrone pellet, the tumors had regressed by 50%, at which time acid phosphatase had increased by 67%, cathepsin by 111%, and 0-glucuronidase by 138%. At Week 2, although levels were decreased compared with those seen at Week 1, values for these enzymes remained elevated. These studies supply additional evidence that lysosomes have some role in tumor regression.