Skin cancer is the most common type of cancer and commonly develops in sun-exposed areas of skin. The incidence is highest among outdoor workers, sportsmen, and sunbathers and is inversely related to the amount of melanin skin pigmentation; fair-skinned people are most susceptible. Skin cancers may also develop years after therapeutic x-rays or exposure to carcinogens (eg, arsenic ingestion).
Over 5.4 million new cases of nonmelanoma skin cancer were diagnosed in 2012 among over 3.3 million people in the United States. (See The Skin Cancer Foundation.)
The most common forms of skin cancer are
The less common forms of skin cancer are
Paget disease of the nipple Paget Disease of the Nipple Paget disease is a rare type of carcinoma that appears as a unilateral eczematous to psoriasiform plaque of the nipple and areola. It results from extension to the epidermis of an underlying... read more
or extramammary Paget (usually near the anus)Tumors of the adnexa
Bowen disease Bowen Disease Bowen disease is a superficial squamous cell carcinoma in situ. Diagnosis is by biopsy. Treatment depends on the tumor’s characteristics and may involve curettage and electrodesiccation, surgical... read more 
is a superficial squamous cell carcinoma. Keratoacanthoma Keratoacanthoma Keratoacanthomas are round, firm, usually flesh-colored nodules with sharply sloping borders and a characteristic central crater containing keratinous material; they usually resolve spontaneously... read more 
may be a well-differentiated form of squamous cell carcinoma.
Initially, skin cancers are often asymptomatic. The most frequent presentation is an irregular red or pigmented lesion that does not go away. Any lesion that appears to be enlarging should be biopsied—whether tenderness, mild inflammation, crusting, or occasional bleeding is present or not. If treated early, most skin cancers are curable.
Screening
Some professional organizations support clinical examination and self-examination to screen for skin cancer; however, the US Preventive Services Task Force has not found sufficient evidence to do so. (See also the US Preventive Services Task Force summary of recommendations for screening for skin cancer and counseling for skin cancer.)
Prevention
Because many skin cancers seem to be related to ultraviolet (UV) exposure, a number of measures are recommended to limit exposure.
Sun avoidance: Seeking shade, minimizing outdoor activities between 10 AM and 4 PM (when sun's rays are strongest), and avoiding sunbathing and the use of tanning beds
Use of protective clothing: Long-sleeved shirts, pants, and broad-brimmed hats
Use of sunscreen: At least sun protection factor (SPF) 30 with broad-spectrum UVA/UVB protection, used as directed (ie, reapplied every 2 hours and after swimming or sweating); should not be used to prolong sun exposure
Current evidence is inadequate to determine whether these measures reduce incidence or mortality of melanoma; in nonmelanoma skin cancers (basal cell carcinoma Basal Cell Carcinoma Basal cell carcinoma is a superficial, slowly growing papule or nodule that derives from certain epidermal cells. Basal cell carcinomas arise from keratinocytes near the basal layer, which are... read more 
and squamous cell carcinoma Squamous Cell Carcinoma Squamous cell carcinoma is a malignant tumor of epidermal keratinocytes that invades the dermis; this cancer usually occurs in sun-exposed areas. Local destruction may be extensive, and metastases... read more 
), sun protection does decrease the incidence of new cancers.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
The Skin Cancer Foundation: Information about skin cancer facts and statistics
American Academy of Dermatology Skin Cancer Resource Center: Consumer-friendly information about finding, treating, and raising awareness for skin cancers
