Chemotherapy of human tumor xenografts in genetically athymic mice

A series of studies were undertaken to evaluate the chemotherapeutic response to various antineoplastic drugs of human breast (MX-1) or colon (CX-2) tumor xenografts growing in genetically athymic (nude) mice. Fragments (2mm³) of either tumor type were implanted subcutaneously into the subaxillary region of NIH Swiss nude mice, and single drug therapy was started when tumors became palpable and were growing progressively. 5-Fluorouracil (5-FU) administered on a Q7DX3 schedule starting on Day 21 post tumor implantation elicited significant retardation in the growth rate of CX-2 tumor. A single treatment with methyl-CCNU induced temporary tumor regression. Against MX-1 tumor, both cyclophosphamide and melphalan induced tumor regressions with no recurrence. 5-FU slowed but did not arrest growth of MX-1 tumor. These tumor systems grown in nude mice appear to be suitable models for in vivo screening of anticancer agents that would prove clinically active.