Tumors in organ transplant recipients may give clues to their control by immunity

Tumors in solid organ transplant recipients are an important complication of surgery. They can be due to the recurrence of malignancy existing in the recipient prior to transplantation, tumors of donor origin transmitted inadvertently and de novo malignancies. These patients constitute a sort of experimental group in whom the normal immune control of the host has been weakened and can provide valuable information. The reported distribution of the tumors developed in these patients may indicate those whose development is controlled by the immune system. Some of the reported data has been unexpected. For example, patients grafted to treat a primary cancer or in whom an asymptomatic tumor was discovered at the time of transplantation rarely have a recurrence. Many of these were skin tumors, but why the SCC/BCC incidence ratio is far from 1 is unclear. Melanomas are not more frequent among immunosuppressed grafted patients, in spite of the fact that they have specific antigens which could be targets for immune and tumor growth control. Some tumors regress and disappear when the immunosuppression regimen is withdrawn. Tumor types rarely observed in grafted patients are thus immune-insensitive and would not normally regress due to immunotherapy.