Comparison of metastasis of mammary tumors growing in the mammary fatpad versus the subcutis.

The frequency with which metastasis occurs for three tumor sublines derived from a single mouse mammary tumor, all of which grow preferentially in mammary fatpads (as compared to the subcutis), was determined from primary tumors growing in mammary fatpads and from primary tumors growing in the subcutis. A relatively metastatic subline was found to metastasize more readily from the mammary fatpad than from subcutaneous sites. The number of metastatic nodules found in the lungs of animals following surgical removal of primary tumors transplanted into intact mammary fatpads was significantly greater than the number of nodules in the lungs of animals following surgical removal of primary tumors transplanted subcutaneously. Two sublines, which do not readily metastasize from tumors growing subcutaneously, did not metastasize from tumors growing in mammary fatpads.