Thin melanomas present diagnostic, treatment dilemmas

December 1, 2010

Treatment algorithms notwithstanding, diagnosing and treating melanomas measuring less than 1 mm thick poses many challenges, an expert says.

Key Points

Philadelphia - Treatment algorithms notwithstanding, diagnosing and treating melanomas measuring less than 1 mm thick poses many challenges, an expert says.

Treating such melanomas appears simple, says Christopher J. Miller, M.D., director of dermatologic surgery and assistant professor of dermatology, University of Pennsylvania School of Medicine. "You find a suspicious lesion; biopsy it, which allows you to make the diagnosis; then you cut it out. But at every step of the way, there are potential pitfalls and places where dermatologists can struggle."

For starters, he says dermatologists biopsy an average of 18 benign lesions for every melanoma they find based on clinical presentation. Technological advances such as dermoscopy, full-body photography and, at a few institutions, in vivo confocal laser scanning microscopy can improve diagnostic accuracy. But all come with limitations.

Regarding biopsies, he says the ideal method for suspicious lesions involves excision to the subcutaneous fat, with a margin of 1 mm to 3 mm around the lesion. However, for a substantial portion of melanomas (such as those on the face), such a biopsy would likely leave a scar.

"One would not want to choose complete excision as the method of diagnosis," especially when some data show that the naked eye correctly diagnoses melanoma in only two of three cases, Dr. Miller says.

Partial biopsies

Other biopsy techniques sample a portion of the lesion. "That leads to challenges, because the biopsy may not have gone deep enough to give you the full depth of the melanoma. Another problem is that if one only samples part of the lesion, that might not be the most aggressive area," Dr. Miller says.

Partial biopsies miss more aggressive portions of tumor up to 20 percent of the time (Karimipour DJ, Schwartz JL, Wang TS, et al. J Am Acad Dermatol. 2005;52(5):798-802; Stell VH, Norton HJ, Smith KS, et al. Ann Surg Oncol. 2007;14(2):893-898. Epub 2006 Nov 21).

Staging criteria

Regarding staging, new American Joint Committee on Cancer (AJCC) criteria emphasize three major microscopic features of a primary melanoma to determine prognosis: melanoma thickness and the presence or absence of ulceration and mitoses (http://www.cancerstaging.org/staging/index.html). Using these criteria, the AJCC has estimated survival curves based on 27,000 patients followed for 10 years.

However, Dr. Miller says these three criteria alone cannot precisely predict survival with certain subgroups of patients with melanoma. "Among patients with thin melanomas, for example, 3 to 8 percent will develop metastases at some time."

Models that use more factors allow physicians to estimate survival more accurately, he says. Examples include Individualized Melanoma Patient Outcome Prediction Tools, a joint effort between the AJCC and the University of Alabama ( http://www.melanomaprognosis.org/). These tools factor in age, gender and melanoma site. Based on AJCC criteria, physicians should offer a patient with a thin melanoma and other risk factors (ulceration, at least one mitosis or invasion into lymphatic or blood vessels) a sentinel lymph node (SLN) biopsy, Dr. Miller says.

"If the patient has a positive SLN biopsy, the standard of care is to recommend a complete lymphadenectomy - removing all the lymph nodes in the chain where the positive biopsy occurred. The dilemma here is that no data indicate that complete lymph node dissection improves survival in these patients. That's especially controversial in patients with thin melanomas," which have yielded contradictory study results in this regard.

"Although many references state as a matter of fact that SLN biopsy status is the strongest prognostic factor compared to any factor on the primary melanoma, the results of SLN biopsies are not clear in patients with thin melanomas (Wong SL, Brady MS, Busam KJ, Coit DG. Ann Surg Oncol. 2006;13(3):302-309. Epub 2006 Jan 30)," Dr. Miller says.