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Skin Cancer in Organ Transplant Patients: From a Side Effect of Social Practice to a Side Effect of Medical Practice

SKIN CANCER has now become one of the common public health problems in people with fair skin living in developed countries. The increased incidence and mortality rates have paralleled changes in fashion for a sun tan and in social values that allow ever-increasing proportions of the body to be exposed while outdoors. This has been associated with increasing leisure time and increased accessibility to follow the sun worldwide. The relationship of skin cancer to sunlight was first recognized in the late 19th century, particularly for basal cell carcinoma and squamous cell carcinoma. It was not until the 1950s that the relationship between sunlight and melanoma was first reported. With increasingly sophisticated epidemiologic studies, it has become apparent that sunlight has been the major environmental risk factor contributing to the development of a skin cancer in those people who are constitutionally predisposed. Epidemiology has also shown that there are probably different exposure patterns required at different times of life to induce the different cancers, that is, basal cell carcinoma, squamous cell carcinoma, and melanoma. There has been a substantial increase also in recent times in our understanding of the role of the immunologic response in control of each of these cancers. At the same time, our increasing knowledge of the immunosuppressive effect of ultraviolet (UV) radiation contributing to the promotion of skin cancer after its induction has been a further addition to our understanding of causation. Along with our increased understanding of the genetic and molecular basis for various components of the immunologic response has come increasing specificity in our ability to control it. This can be either in those cases when the immunologic response is occurring aberrantly, for example, in autoimmune disease, or when we want to prevent it acting normally, in the case of organ transplantation. In the latter case, this has led to an exponential increase in the number and type of organs being transplanted. Successful grafts now commonly last decades in a substantial proportion of patients who have had transplantation. Of course, being a relatively expensive and complicated procedure, it has occurred mainly in developed countries, those countries populated by fairskinned people where skin cancer incidence has also been on the rise. Of the three common skin malignancies, squamous cell carcinoma fits best with the classical cancer epidemiology of dose response to a carcinogen (UV radiation). This keratinocyte tumor also fits well with the model of immunogenicity with its control being dependent on an intact immunologic response. Little wonder therefore that at the beginning of the 21st century, organ transplantation has the potential to create an extra dimension in the public health problem of skin cancer load. This is particularly for squamous cell carcinoma and related keratinocyte dysplasias. So, now we have a problem—what are we going to do about it? There is an established model that has been used in the public health approach to behaviorrelated skin cancer. That has been to define first exactly the nature and extent of the skin cancers, who is getting them, what is leading to their development, and what can one do about them. For the transplant population, there is a need for an epidemiologic approach not only for who gets these tumors and at what stage after transplant (some of this research has been done already) but also, and more critically, exactly what is the true extent of the health burden produced by these tumors. For example, no one has been able to report with accuracy exactly how many tumors have occurred in any given transplant population over time. What is most likely to have been reported is the time at which they get the tumors. Eventually, so many of these patients develop such large numbers of tumors that people stop recording the exact number and thus we do not have accurate figures on the true burden. It means that we have to record each and every tumor these patients develop—a potentially demanding but critical task that one could predict will show that the burden produced by the absolute number of