SANTA BARBARA, CALIF. — The melanomas that students are taught to recognize in medical school are often tough to miss—ugly, misshapen, and black, maybe with tinges of blue and red.
In real life, it's not always that easy, Clay J. Cockerell, M.D., said at the annual meeting of the California Society of Dermatology and Dermatologic Surgery.
“This disease will teach you a lot,” said Dr. Cockerell, president of the American Academy of Dermatology and professor of dermatology and pathology at the University of Texas Southwestern Medical School in Dallas.
Prototypic, evil-looking melanomas do exist, but generally they herald metastatic disease. And while the ABCDs—and now “E” for evolution—can help identify melanomas sooner, the sensitivity for diagnosis by clinical appearance alone still hovers between 48% and 67% in most studies.
“I'd be willing to bet almost every person in this room has missed a melanoma clinically at least once in their career,” Dr. Cockerell surmised.
The diagnostic challenge is only getting more difficult, he said.
“In my own experience looking at hundreds and hundreds of slides under the microscope, there's no question we're seeing far more melanomas than we used to. We're also seeing melanoma at smaller stages in evolution and melanoma that has unusual features,” he said.
These days, if it's black and asymmetrical, “to me, it's melanoma until proven otherwise,” no matter its size, Dr. Cockerell said.
Some entities that can mimic melanoma include a halo nevus, solar lentigo, traumatized blue nevus, seborrheic keratosis, pigmented basal cell carcinoma, pigmented Bowen's disease, pigmented squamous cell carcinoma, and thrombosed angioma.
In a study of 1,784 histologically proven primary melanomas, Dr. Cockerell and associates found 583 that were not clinically suspicious. In these “wolf-in-sheep's-clothing” cases, the presumed diagnoses included nevi, basal cell carcinoma, Bowen's disease, pigmented seborrheic keratosis, and lentigo, among others (Am. J. Dermatopathol. 1991;13:551–6).
Unfortunately, the histologic diagnosis can be murky as well.
Spitz nevus is a well-known mimicker of melanoma, although Dr. Cockerell uses the “Mary Poppins rule” to decide on management. A Spitzlike lesion in a child must be “practically perfect in every way” in terms of meeting criteria for melanoma to draw Dr. Cockerell's concern, while in an adult, the opposite is true.
More perplexing is desmoplastic malignant melanoma, which may have a very “banal” appearance both clinically and under the microscope, he said.
In such a case, characteristic spindle cells may be scarce, while the overall picture is of minimal cytologic atypia. A key to identifying it is nesting within the epidermal component, Dr. Cockerell said.
Photos courtesy Dr. Clay J. Cockerell
Answer Key:
1. irritated blue nevus; 2. nodular melanoma; 3. melanoma with halo; 4. dermatofibroma; 5. pigmented basal cell carcinoma; 6. halo nevus; 7. pigmented basal cell carcinoma; 8. pigmented Bowen's disease