Relationship between tumor growth characteristics and preferential sites of growth.

The anterior-posterior incidence of spontaneous mammary tumor development and the anterior-posterior gradient of growth potential among transplanted tumors was studied in C3H/He and C3Hf/He mice. The relative incidence of spontaneous tumor development in the five mammary gland pairs showed no anterior-posterior bias, but it was in proportion to the quantity of tissue in the individual mammary glands. The transplantability and growth rate of 164 spontaneous C3H/He and 67 spontaneous C3Hf/He mammary carcinomas were tested and compared in anterior and posterior subcutaneous sites and at mammary implantation sites. Initially, in their early transplant generations, most subcutaneous tumor implants (67%) grew significantly better near the shoulder than in an implantation site near the hip. At the same time, implants from the same tumor tissue grew equally well in anterior (#2) and posterior (#4) mammary glands. Without exception, all transplanted tumors grew better in a mammary gland than at a subcutaneous site. Some tumors (12%) that initially would grow only in mammary glands gained subcutaneous transplantability with increased growth rate. With increasing growth rate, the tumors' anterior subcutaneous growth preference decreased. Anterior subcutaneous growth preference was not related to immunologic tumor characteristics. Implants of slow-growing tumors grew better in the anterior subcutaneous implantation site where the greater blood flow improved their growth conditions and survival rate.