Immunohistochemical Localization of Catechol Methyltransferase in Normal and Cancerous Breast Tissues of Mice and Rats

: The immunocytochemical localization of catechol methyltransferase was determined in normal and cancerous breast tissues of inbred female Swiss-Webster mice and in normal, lactating, and cancerous breast tissues of inbred Sprague-Dawley rats. The enzyme was found to be cytoplasmically localized in ductal epithelial cells of secretory tubules in both inactive and stimulated mammary glands, in endothelial cells lining blood vessels, in fibroblasts in the connective tissue matrix, and, especially, in tumor cells. Adipose cells were nonreactive. The intensity of the immunocytochemical reaction in tumor cells was stronger than that in lactating tissues, which, in turn, was more reactive than that in normal, unstimulated breast tissues.