Accelerated appearance of neoplasms in female NZB/NZW mice treated with high-dose cyclophosphamide.

Prolonged immunosuppressive therapy with cyclophosphamide increases the prevalence of neoplasms in NZB/NZW mice, an animal model of systemic lupus erythematosus. The current study was designed to compare the oncogenic properties of high dose cyclophosphamide with a low dose therapeutic regimen. Female NZB/NZW mice received life-long therapy with "high dose" cyclophosphamide, 16 mg/kg/day, or "low-dose" cyclophosphamide, 5.7 mg/kg/day; control mice received saline. High dose therapy clearly accelerated appearance of neoplasms. Seventeen of 19 mice treated with high-dose cyclophosphamide developed neoplasms at the mean age of 61 weeks. Fifty-seven percent of these tumors were mammary carcinomas. Neoplasms appeared in all mice treated with low dose; mean longevity in this treatment group was 80 weeks (compared to high dose treated mice, P less than 0.001). Carcinomas, pulmonary adenomas, and lymphomas were the most common tumors in mice receiving low dose therapy. Positive tests for ANA were suppressed in high dose treated mice. AntiDNA antibody levels and glomerulonephritis were decreased significantly in both groups of cyclophosphamide-treated mice compared to controls. It was concluded that the high daily dose of immunosuppressive drug was related to early oncogenesis in autoimmune NZB/NZW mice.