Enhancement of mammary tumor formation in mice by a cytostatic drug, melphalan.

Melphalan (L-phenylalanine mustard), a cytostatic drug used in treatment of human breast cancer, was injected into mice bearing preneoplastic hyperplastic alveolar nodule mammary outgrowth line D2. Melphalan, doses of either 2.5 or 5.0 mg/kg, markedly enhanced tumor formation in its mammary nodule outgrowth line. Samples of nodule outgrowths in untreated mice produced 13% tumors by 9 months after transplantation, whereas nodule outgrowths in melphalan-treated mice produced 57 and 85% mammary tumors in the lower and higher dose groups, respectively.