Cancer and teratogenesis: infrequent occurrence after medical use of immunosuppressive drugs.

This study examines long term "medical" immunosuppression with azathioprine or cyclophosphamide for immunopathic disease in relation to cancer and foetal malformation. The experience represent an aggregate of 241 years of treatment and 508 patient-years of follow-up in 133 non-transplant patients. For azathioprine the mean duration of treatment was 1-9 years and the mean duration of observation was 3-8 years, and for cyclophosphamide, the mean durations of treatment and observation were 0-7 and 4-6 years. A sample of 70 patients was shown by in vivo tests to have significantly suppressed cell-mediated immunity. In the period of review there were observed two cancers, both squamous cell carcinomas of skin, two benign neoplasms and six keratoses; after the period of review, three further cancers were recorded, one being in a subject with a known previous cancer. Nine pregnancies with azathioprine yielded no foetal malformations.