- Expect to encounter 6 to 7 cases of basal cell cancer, 1 to 2 cases of squamous cell cancer, and approximately 1 case of melanoma ever y year.
- There is good evidence for using the American Cancer Society’s ABCDE criteria as a clinical diagnostic test to rule out malignant melanoma (A).
- The revised 7-point checklist has high sensitivity and is therefore useful for ruling out a diagnosis of malignant melanoma. However, its low specificity yields many false-positive results (B).
- The gold standard for diagnosis of skin malignancies is a tissue biopsy. If any doubt exists about the diagnosis, a biopsy should be performed (A).
The American Cancer Society’s ABCDE criteria and the revised 7-point checklist are the most reliable means of detecting or ruling out malignant melanoma. Each has its strengths and weaknesses, a knowledge of which will increase the accuracy of assessment and minimize chances of misdiagnosis.
In addition to these 2 clinical prediction rules, we examine the evidence on physician’s global assessment of nonmelanoma skin cancers and review the risk factors for the major types of skin cancer. As a result of a comprehensive evidence-based review on the incidence, risk factors, and diagnosis of skin malignancies, we present an algorithm for evaluating skin lesions.
Impact of skin cancer
The incidence of malignant melanoma has increased from 1 in 1500 in 1930 to 1 in 75 for the year 2000.1 Although it is the rarest skin cancer (1% of skin malignancies), it is also the deadliest, accounting for 60% of skin cancer deaths.2
Nonmelanoma skin cancers, which include squamous cell cancers and basal cell cancers, account for one third of all cancers in the United States. Approximately 1 million cases were diagnosed in 1999.3 Deaths from nonmelanoma skin cancers are in steady decline, and the overall 5-year survival rate is high (over 95%).4 Recurrent nonmelanoma skin cancer, however, carries a very poor prognosis, with only a 50% cure rate.5
Treatment of nonmelanoma skin cancer costs over $500 million yearly in the US.4
Primary care physicians help improve prognosis
More persons visit primary care physicians (38.2%) than dermatologists (29.9%) for evaluation of suspicious skin lesions.6 Such lesions are usually benign, but a malignancy must be excluded. A primary care physician can expect to diagnose 6 to 7 cases of basal cell cancer, 1 to 2 cases of squamous cell cancer, and approximately 1 case of melanoma every year, according to population-based studies.4
Primary care practitioners contribute to a more favorable prognosis. For each additional family physician per 10,000 population, the chances of diagnosing malignant melanoma earlier increase significantly (odds ratio= 1.21, 95% confidence interval, 1.09–1.33, P<.001).7
Primary care physicians who diagnose non-melanoma skin cancers can select therapies that offer maximum efficacy and cost-effectiveness.
According to a study of 1215 biopsies conducted in a primary care population, over 80% of biopsied lesions were benign and included nevi, seborrheic keratoses, cysts, dermatofibromas, fibrous histiocytomas, and polyps or skin tags. Pre-malignant lesions (including actinic keratoses and lentigo maligna) represented 7% of the total. Thirteen percent were malignancies: basal cell carcinomas (73%), followed by squamous cell carcinomas (14%), and malignant melanomas (12%). One metastatic adenomacarcinoma was included in the series (1%) (level of evidence [LOE]: 4).8
The differential diagnosis for basal cell carcinoma includes superficial basal cell carcinoma, pigmented basal cell carcinoma, infiltrating basal cell carcinoma, tricoepithelioma, keloid, molluscum contagiosum, and dermatofibromas.
For squamous cell cancer, the differential includes squamous cell carcinoma, keratoacanthoma, eczema and atopic dermatitis, contact dermatitis, psoriasis, and seborrheic dermatitis.
The differential diagnosis for malignant melanoma includes seborrheic keratosis, traumatized or irritated nevus, pigmented basal cell carcinoma, lentigo, blue nevus, angiokeratoma, traumatic hematoma, venous lake, hemangioma, dermatofibroma, and pigmented actinic keratosis.
Using the history and physical examination
Nearly 70% of melanomas are discovered by patients or their family (LOE: 4).9 Patients may express concern about changed size or appearance of a lesion; associated pain, pruritis, ulceration, or bleeding; location in a cosmetically sensitive area; or worry voiced by a family member. Additionally, a patient may have a family or personal history of skin malignancy, history of skin biopsy, or predisposition to sunburns.
Nurses and physicians identify lesions before a patient does approximately one quarter of the time while examining a patient for an unrelated condition or as part of a comprehensive work-up (LOE: 4).9
Types of skin malignancies
See Photo Rounds, page 219, for images of many types of skin cancer.
Basal cell carcinoma
The patterns of basal cell carcinoma are nodular, superficial, micronodular, infiltrative, morpheaform, and mixed.10 They may be pigmented and are sometimes misdiagnosed as melanoma.11 However, most basal cell carcinomas are typical in appearance and easily diagnosed by visual and tactile inspection.