Effect of medroxyprogesterone acetate on the growth of mouse transplanted tumors: relation with hormone sensitivity

The effect of high and low doses of medroxyprogesterone acetate (MPA) was investigated on three transplanted murine tumors (MXT mammary carcinoma, colon 38, and colon 26) in relation to receptor status and sensitivity of the tumors to ovariectomy and treatment with dexamethasone. MPA had no inhibitory activity on the growth of these tumors. It had no effect on the ovarian-sensitive MXT tumor; it significantly enhanced the growth of an MXT tumor line, selected through serial transplantations, which was stimulated also in ovariectomized animals. MPA, as well as ovariectomy, stimulated the growth of the colon 38 tumor, but this hormone sensitivity was lost during serial transplantations. No correlation was found between the effects of MPA and ovariectomy and the steroid receptor status of these tumors. MPA effects on these tumors do not seem contingent upon a glucocorticoid-like action since dexamethasone was highly effective on all the tested tumors. The combined treatment of the colon 26 tumor with a cytotoxic drug, 4'-deoxydoxorubicin, and MPA, which administered alone stimulated tumor growth and increased life span, caused a slight increase in the life span compared to single agents alone.