On the rise: Aggressive skin cancers can be easily overlooked

October 1, 2008

An expert says dermatologists must be careful not to overlook or misdiagnose four aggressive skin cancers whose incidence rates are rising - lentigo maligna, atypical fibroxanthoma, Merkel cell carcinoma and high-risk squamous cell carcinoma.

Key Points

"MCC is an unusual cancer that we're seeing more of. Lentigo maligna is more common but a challenge to treat because of the difficulty in getting clear margins," says Marc D. Brown, M.D., professor of dermatology, University of Rochester Medical Center, Rochester, N.Y.

Although the percentage of organ transplant recipients who develop high-risk SCCs is relatively small, the number of organ transplant recipients overall is growing, as is their life expectancy, he says.

By definition, LM is a melanoma in situ that often extends well beyond what a physician can see clinically.

Therefore, Dr. Brown says, "Taking the typical 5 mm excision margin usually will not be enough."

However, clinical challenges arise because physicians are unable to predict if and when LM will progress to lentigo maligna melanoma, Dr. Brown says.

"The biggest challenge with LM is that the lesions are often located on the face, and they can be very large and ill-defined. And they're often in very important cosmetic areas," he adds.

Modified Mohs

Dr. Brown treats LM with the modified Mohs technique, with rush permanent sections.

Rather than using frozen sections, this technique involves having the dermatopathologist produce permanent paraffin-embedded sections, which Dr. Brown's practice gets one day after the tissue samples have been excised.

"Within 24 hours," he says, "we can tell the patients whether they need to have more excised or not."

More specifically, using mapping techniques common to Mohs surgery, "We carefully track out any peripheral extension of the cancer. By doing that, we get high-quality slides, good backup from our dermatopathologists and high success rates (1 to 2 percent local recurrence)," Dr. Brown says.

Most pathologists feel permanent sections provide a more accurate way to diagnose LM than frozen sections do, Dr. Brown tells Dermatology Times.

However, he says the modified Mohs technique is somewhat controversial because some Mohs surgeons perform typical Mohs surgery with frozen sections for LM.

"But many Mohs surgeons, like myself, still believe that using the peripheral mapping technique of Mohs surgery, but having permanent sections made, is, at least in our hands, an accurate way of treating LM," Dr. Brown says.

Nonsurgical options

Nonsurgical options for LM include radiation and imiquimod. However, a recent analysis of four open-label studies and 11 case reports found that without controlled studies and prolonged follow-up, "The use of imiquimod for LM must still be considered experimental [Rajpar SF, Marsden JR. Br J Dermatol. 2006 Oct;155(4):653-656]."

Somewhat similarly, Dr. Brown says experts advise considering radiotherapy for LM only in patients who aren't surgical candidates (Farshad A et al. Br J Dermatol. 2002 Jun;146(6):1042-1046).

"AFX is believed to have a very low incidence of metastatic spread, yet we've reported six patients now who have developed metastatic AFX," of a total of 15 metastatic cases reported in medical literature, Dr. Brown says.

However, he says dermatologists rarely diagnose AFX correctly preoperatively.

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