Overview of Skin Cancer

By Gregory L. Wells, MD, Dartmouth Medical School and Dartmouth-Hitchcock Medical Center

NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version

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 skin cancer are diagnosed in over 3.3 million people in the US yearly. (See The Skin Cancer Foundation and also the US Preventive Services Task Force summary of recommendations for screening for skin cancer and counseling for skin cancer.)

The most common forms of skin cancer are

Basal cell carcinoma (about 80%)
Squamous cell carcinoma (about 16%)
Melanoma (about 4%)

The less common forms of skin cancer are

Paget disease of the nipple or extramammary Paget (usually near the anus)
Kaposi sarcoma
Merkel cell carcinoma
Atypical fibroxanthomas
Tumors of the adnexa
Cutaneous T-cell lymphoma (mycosis fungoides)

Bowen disease is a superficial squamous cell carcinoma. Keratoacanthoma 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.

Pearls & Pitfalls

Biopsy any skin lesion, whether appearance is typical for cancer or atypical, that enlarges or persists longer than expected.

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 h 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 and squamous cell carcinoma), sun protection does decrease the incidence of new cancers.