The skin, the largest organ in the body, protects the body from outside pathogens, regulates body temperature, maintains water balance, performs sensory perception and produces vitamins and hormones. As the body’s first line of defense against microbes, viruses and ultraviolet radiation, the skin is vulnerable to damage. Two common types of skin cancer--the abnormal growth of skin cells—include squamous cell carcinoma and basal cell carcinoma. Although these cancers share some characteristics, such as both occurring due to sun exposure and classified as keratinocyte cancers, they also exhibit differences.
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Frequency of Diagnosis
Basal cell carcinoma, the most common form of skin cancer, accounts for approximately 8 out of 10 skin cancers, as reported in March 2010 by the American Cancer Society. Basal cell carcinoma affects approximately 1 million Americans per year, and squamous cell carcinoma, the second most common type of cancer, causes more than 250,000 new cases of skin cancer each year, according to information released in 2010 from the Skin Cancer Foundation.
Affected Skin Cells
The skin consists of three layers: the top layer known as the epidermis; the inner layer, known as the dermis; and the fatty subcutaneous layer. The deepest layer of the epidermis, known as the basal layer, contains basal cells that produce keratinocytes—cells that produce the protein keratin. Basal cell carcinoma begins in the basal cells. Basal cell carcinoma most commonly affects areas of the body exposed to environmental factors including the face, ears, neck, scalp, shoulders and back.
Squamous cell carcinoma affects the squamous cells—flat cells found in and just under the outer most layer of the epidermis known as the stratum corneum. Squamous cell carcinoma, commonly found on the face, ears, lips, back of hands and neck, can also occur in scars and skin ulcers in other parts of the body, as well as in the genital area.
Appearance of Lesions
In addition to keeping exposed areas of skin protected, watching for changes in the appearance of skin or the formation of any unusual bumps or nodules is important. Signs of basal cell carcinoma include the appearance of a pearly or waxy looking bump. Basal cell carcinoma may also look similar to a scar, appearing as a flesh-colored or brown flat unusual area. Squamous cell carcinoma often begins as a firm red-colored nodule. It can also remain flat, but the surface looks scaly and crusty.
Rate of Growth
Basal cell carcinoma cancer cells grow slowly. This type of cancer rarely spreads to nearby lymph nodes or other parts of the body. Squamous cell carcinoma, however, is aggressive and often invades the fatty subcutaneous layer, spreading to nearby lymph nodes and distant organs in the body.