Tips for making an accurate diagnosis
Basal cell carcinoma and melanoma can mimic other lesions, so keep these tips in mind:
- The “company” a lesion keeps sometimes can help in diagnosis. A patient may have a group of small “pearly papules,” only one of which may show the typical umbilication that allows a confident diagnosis of molluscum contagiosum, for example. Here, 3 lesions had similar dermoscopic structures, only one of which exhibited telangiectasia. A fourth lesion lacked diagnostic characteristics. The best guess, based on the sum total appearance of all of these lesions, is that all are basal cell carcinomas because of the “company they are keeping”—but note that this is also potentially a trap: missing the single basal cell carcinoma lesion among a field of sebaceous hyperplasia, for instance.
- Don’t focus exclusively on the symptomatic lesion. Do a survey of the general region. For ultraviolet-associated lesions (including basal cell carcinoma), it’s preferable to perform, at minimum, a survey of “high-radiation” areas (face, exposed scalp, neck, ears, and dorsal hands and forearms) for other ultraviolet “damage” (eg, actinic keratoses).
- Be meticulous when examining patients’ backs. Patients may not spot lesions on their backs—especially if they are older and have poor vision.
- Avoid thinking in terms of absolutes like “never” and “always.” The clinical axiom that basal cell carcinomas “never” have hair growing from them is disproved by (FIGURE 3A), which clinically, dermoscopically, and histologically is a basal cell carcinoma lesion. Some of the hair seen here is overlying, loose scalp hair “caught” in the dermoscopic field because of the location of this lesion on the temple adjacent to the hairline. But there are also very distinct hairs seen coming out from areas (at about 6 and 8 o’clock) that are clearly part of the lesion, especially on its periphery.
When in doubt, biopsy
When in doubt about which technique to perform, do an incisional biopsy—preferably excisional, but at least a good sampling of the most worrisome area(s).
Suspected basal cell carcinoma, when the examiner is confident the lesion is not a melanoma, can be further evaluated by superficial shave biopsy. Potential melanoma generally should not be evaluated by the shave technique.