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Detecting Skin Cancer

Summarized By: Robert W. Griffith, MD

Surprisingly, skin cancer is the commonest human malignancy in the USA, and the incidence is increasing. Accurate, early diagnosis can reduce morbidity and mortality dramatically, while improved prevention can make inroads into the escalating incidence. The most frequent types are melanoma, basal cell carcinoma (BCC), and squamous cell carcinoma (SCC).

Melanoma

Although less common than BCC and SCC, melanoma carries a high mortality rate, and therefore usually receives more attention. Melanomas account for 2% to 3% of all cancers in the USA, and its frequency doubles every ten years. Young people are often affected -- it's the commonest malignancy in white adults between 25 and 29 years. About 15% of melanoma patients die from the disease, 20% of them being under 40.

Mortality is directly related to the depth of invasion at identification, emphasizing the importance of early diagnosis. As with BCC and SCC, the ultraviolet radiation of sunlight is well established as an etiological agent. However, in the case of melanoma, there is no obvious relationship to chronic exposure, while intense, intermittent exposure is highly correlated. This sort of exposure occurs in children with severe sunburns.

There are host factors for all types of skin cancers; fair skin, blue eyes, red hair, freckles, and a tendency to burn rather than tan, all of which represent a lessened degree of pigmentation, are recognized risk factors.

Pigmented naevi are the strongest predictors of risk of melanoma -- the greater the number, the higher the risk. 30% of melanomas arise in pre-existing moles. It should be noted, however, that the presence of freckles and naevi might reflect the degree of solar exposure in predisposed people. A family history of melanoma is also a risk factor, so that the occurrence in a first-degree blood relative increases the risk 8-fold.

There are 4 types of malignant melanoma:

Type Frequency Characteristics

Superficial spreading 70% Adults, anywhere (upper back, legs)

Nodular malignant 15% - 30% Domed or pedunculated, very invasive

Lentigo maligna 4% - 10% Slow growing, horizontal/radial lines

Acral lentiginous 2% - 8% Palms and plantar surfaces, digits, nails

Diagnosis is dependent on the history and the appearance of the lesion. The ABCD approach is well-tried: Asymmetry, Border irregular, Color variation, & Diameter over 6 mm are useful features to evaluate. Bleeding, burning, or itching raise suspicion further. Tumor thickness is the single most important prognostic indicator of the patient's survival.

Distinguishing pigmented lesions can be difficult. Mimicking lesions include: seborrheic keratoses, congenital naevi, and benign acquired naevi. Not all unusual looking moles are melanomas, and the decision to excise or biopsy is not always clear-cut. If the history and appearance of the lesion, together with a family history, give rise to suspicion, a full-thickness biopsy is warranted -- an elliptical incision including 1 to 2 mm of normal skin with extension to the subcutaneous tissue is advised.

Secondary features -- involvement of surrounding skin, underlying tissues, and regional lymph nodes -- are important for assessing the prognosis. And, of course, a full-body search for other lesions must be done.

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Basal Cell Carcinoma
This is the most common skin neoplasm. The typical appearance of a basal cell carcinoma is that of a nodular-ulcerative lesion with a raised, rolled, pearly white border. Telangiectasia and crusting can occur. Lesions are seen mostly on the head and neck. If pigmented, a BCC may be confused with a melanoma, while a superficial BCC can resemble a patch of dermatitis. A sclerosing type can extend beyond the clinically assessed borders, and is difficult to treat adequately.

Biopsy is essential for diagnosis. BCCs grow slowly, and rarely metastasize. Simple excision with a 2 to 5 mm margin of healthy skin results in a cure in 95% to 99% of cases.

Squamous Cell Carcinoma
This is the most common skin tumor in elderly people, and usually results from a lifetime exposure to solar radiation. SCCs often occur at the site of previous actinic keratosis - the development of pain, erythema, ulceration, induration, or hyperkeratosis should give rise to suspicion. As with BCCs, most SCCs occur on the head or neck; other sites include the hands, forearms, upper trunk and lower legs.

The appearance may be nodular or papular, reddish-brown or pink, crusted or eroded. When stretched, a definitive edge may be difficult to demonstrate (as opposed to a BCC). The differential diagnosis includes actinic keratosis, amelanotic melanoma, BCC, healing wounds, warts, or keratoacanthoma. A full-thickness biopsy is necessary to make the diagnosis, and small lesions (<2 mm diameter) can be cured by surgical excision - margins of 4 to 6 mm are normally recommended.

Growth may be rapid, and 2% to 6% of SCCs metastasize to the regional lymph nodes, lungs or liver. Once metastasis has occurred, the 5-year survival rate is 34%.

Reducing the burden
To attack the burden imposed by the increasing frequency of malignant skin tumors, attention must be directed to earlier diagnosis, and prevention of the main causative event -- exposure to solar radiation. The second topic is considered in a separate article -- see link below.

A picture is worth a hundred words, especially when it comes to trying to describe different skin lesions. So go to the online Atlas of Dermatology -- see the link below -- to check up on your diagnosis.

Sources
Overview of skin cancer detection and prevention for the primary care physician. AJ. Bruce, DG. Brodland, Mayo Clin Proc, 2000, vol. 75, pp. 491--500

Early detection and treatment of skin cancer. AF. Jerant, JT. Johnson, CD. Sheridan, TJ. Caffrey, Am Fam Physician, 2000, vol. 62, pp. 357--368