By Peter Galvin, MD
Skin cancer is the most frequently diagnosed cancer in the U.S. and worldwide. Nonmelanoma skin cancers, also called keratinocyte carcinomas, are the most common type of cancer treated in the U.S., with more than five million cases a year. Precise estimates are difficult to obtain because, for some reason, keratinocyte carcinoma is not reported in national cancer registries. Basal cell carcinomas are the most common type of keratinocyte carcinoma, followed by cutaneous squamous-cell carcinoma, with more than one million cases per year. That outnumbers all top five reportable cancers treated in the U.S. combined. But unlike basal cell carcinomas, which spread locally on the skin and do not invade the skin or cause distant spread, squamous-cell carcinomas do invade the skin and spread distantly (metastasize). Even though they do metastasize, squamous-cell carcinomas, if caught early, have an excellent prognosis. Nodal metastasis (spread to local lymph nodes) occurs in 1.9 to 5.2% of cases, and overall mortality is 1.5 to 3.4%. However, among immunosuppressed individuals, the risk from these cancers is increased by a factor of 65 to 250. Cutaneous squamous-cell carcinoma accounts for an increasing number of deaths in the U.S., with estimates suggesting that the absolute number of deaths from it is equal to or exceeds those for melanoma or leukemia.
Cutaneous squamous-cell carcinoma accounts for 20% of all skin cancers, and the worldwide incidence is rising. This is thought to be due to an aging population, higher levels of sun exposure, the use of tanning beds, and increased focus on skin cancer screening and detection. It is more common in men than women (3:1 ratio) and five to 10 times more common in those 75 years of age and older vs. those 55 and younger. It usually presents as a scaly, red, or bleeding lesion, often in sun-exposed areas. The incidence is 150 to 360 cases per 100,000 non-Hispanic white people and three cases per 100,000 in black people. The most important risk factor is exposure to ultraviolet radiation, but there are genetic factors such as inherited characteristics like light skin, red or blonde hair, and light-colored eyes. A family history of it increases the risk by a factor of two to four.
Treatment usually involves surgical removal of the primary tumor, usually using local anesthetic. The most common technique involves Mohs surgery, in which the removed piece is immediately examined and, if it is determined that the tumor is extending to the edge of the specimen, additional tissue is removed until all the edges are tumor-free. In the case of squamous-cell tumors, if it is determined that the tumor has invaded deeper tissues and/or local nerves, then multidisciplinary consultation is recommended and radiation therapy and/or adjuvant (chemo) therapy may be advised. Once the tumor has been successfully removed and treated, close surveillance is advisable because recurrence is common, occurring 70 to 80% of the time within two years. Special populations, such as organ-transplant recipients, those with chronic lymphocytic leukemia (CLL), HIV infection, and other forms of immunosuppression warrant heightened surveillance. There has been some success in preventing reoccurrence using oral nicotinamide and retinoids, and topical treatments for early lesions using fluorouracil cream and phototherapy. The use of HPV vaccine is off label and currently controversial.
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