There is evidence that the immunologic system provides a "surveillance" function1 by which neoplastic cells are identified and either eliminated or restricted. Tumorspecific antigens identify the cells as foreign. Patients on immunosuppressive therapy might not recognize these antigens and, thus, have a greater risk of neoplasia. This theoretical consideration has support in the study of McKhann,2 who found an incidence of malignancy "de novo" in patients who had renal transplants of 13:2000. He compared this with an incidence of 8.2:100,000 in the population at large under the age of 40 years. Several reports of malignancy (lymphomas and carcinomas) in renal homotransplants have been published,2-11 and in these instances, it was possible to rule out transplanted neoplasia which has also been described.12-17 The following is a description of two instances of carcinoma of the lower lip in renal homotransplant recipients.
—A 27-year-old man