In the first 3 cases, the initial disorder was a renal problem (glomerulonephritis, renal homograft). The development of secondary neoplasms appeared to be related to long term immunosuppressive therapy. By contrast, in the fourth case the primary disease was already malignant in nature (breast neoplasm) and treatment was mixed (radiotherapy and chemotherapy). In the light of these cases, the risks of treatment using immunosuppressive chemotherapy should not be neglected.