By Ramsey Hachem, M.D.
Washington University School of Medicine Barnes-Jewish Hospital
Division of Pulmonary and Critical Care
February, 2007
Skin cancers are broadly divided into two groups: melanoma and nonmelanoma skin cancer. The latter are the most common cancers in the general population and consist of basal cell and squamous cell carcinomas. Skin cancer received a fair amount of attention in the media recently when First Lady Laura Bush reported that she had a squamous cell carcinoma excised from her leg in the fall. Incidentally, Barbara Bush had a basal cell carcinoma that was removed in 1990 and George Bush had a basal cell carcinoma removed when he was Vice President in 1986. These cases highlight how common these cancers are in the general public. In fact, data from the American Cancer Society suggests that there are over a million new cases of skin cancer annually in the United States, and the majority is basal cell carcinomas.
In general, the risk factors for the development of nonmelanoma skin cancer include ultraviolet light exposure, radiation treatment, immunosuppression, and the chronic use of steroids. Ultraviolet light can cause mutations in the skin cells’ DNA and failure to repair these genetic alterations can result in tumor formation. Certain genes are known to suppress tumor growth and are called tumor suppressor genes. Ultraviolet light, among other insults, can inactivate such tumor suppressor genes and this can result in tumor genesis. Similarly, therapeutic radiation increases the risk of skin cancer formation. Immunosuppressive therapy has long been recognized as a risk for cancer in general, and skin cancers are most common. It is thought that the immune system has a role in detecting and eradicating pre-cancerous lesions. In addition, certain viruses are known to be carcinogenic, especially under the influence of immunosuppression. For example, Epstein-Barr virus, which causes infectious mononucleosis in otherwise healthy adults and adolescents, can cause lymphoma in transplant recipients. Recently, an association between skin cancer and human papillomavirus (HPV) has been suggested, although it is not clear that the virus causes skin cancer.
Skin cancer in transplant recipients differs in a number of ways from the general public. First, the most common skin cancer in transplant recipients is squamous cell carcinoma, whereas basal cell carcinomas are much more common in non-transplant patients. In fact, squamous cell carcinomas occur approximately 100 times more frequently among transplant recipients than the general public. In addition, the skin cancers tend to be more aggressive and more likely to recur after resection among transplant recipients probably because of the ongoing need for immunosuppression. Lastly, skin cancers develop at a younger age among transplant recipients compared to the general public. Therefore, dermatologic surveillance is paramount after transplantation, and suspicious lesions should be evaluated by a dermatologist. Furthermore, since the immunosuppressive regimen is essential after transplantation, the best prevention is minimizing sun exposure.
Melanoma is the sixth most common cancer in the United States and the incidence has been increasing worldwide over the past thirty years. The reason for the increasing incidence is uncertain, but some have proposed that ozone depletion may be increasing our exposure to ultraviolet light. Additionally, changes in the recreational pattern of sun exposure may also contribute to this rising incidence. Risk factors for melanoma include ultraviolet light exposure, a family history of melanoma, multiple nevi, and immunosuppression. Unfortunately, melanoma often has a more aggressive course than nonmelanoma skin cancers (basal cell and squamous cell carcinomas) and is more likely to be invasive and metastatic to visceral organs such as the lungs, liver, and brain. The following features raise the suspicion for melanoma: an asymmetric skin lesion, one with irregular borders, one with different colors, enlargement over time, and size over 6 millimeters. Some have advocated that people at risk for melanoma, including transplant recipients, should examine themselves on a monthly basis in a manner similar to breast self-examination because early detection of melanoma can be life saving.
So, as spring and summer approach, what are we to do? Minimizing sun exposure is paramount. As the old adage goes, an ounce of prevention is worth a pound of cure. The ample use of sunscreen with a high sun protection factor (SPF) is indispensable when sun exposure is unavoidable. Other simple but useful measures include avoiding the mid-day sun, wearing a hat, and long sleeve shirts and pants, if the weather allows. Most importantly, if a skin lesion is detected, it should be evaluated by a physician and probably referred to a dermatologist.