Desmoplastic melanoma

March 7, 2009

San Francisco - Although desmoplastic melanoma represents less than 2 percent of all melanomas, dermatologists should know how to recognize and treat it, because it's frequently misdiagnosed, an expert says.

San Francisco

- Although desmoplastic melanoma represents less than 2 percent of all melanomas, dermatologists should know how to recognize and treat it, because it's frequently misdiagnosed, an expert says.

Researchers divide desmoplastic melanoma (DM) into pure (primarily fibrotic) and mixed varieties, which include features common to conventional melanoma and desmoplastic areas, says Julia Padgett, M.D., assistant professor of dermatology, University of Virginia, Charlottesville, Va.

"Due to a lack of distinctive clinical presentation features, DM is not often diagnosed prior to biopsy. At the time of an incisional or excisional biopsy, a hard or gritty feeling to the skin may be the first indication that a fibrotic tumor is present." Histologic diagnosis is rarely straightforward either, she says.

She says that because survival rates for patients with distant metastases are poor, studies emphasize the importance of excision with wide margins, namely one to 2cm. Experts favor 2 cm "because recurrence rates are significantly higher when margins of less than 1 cm are used.

"And for DM’s arising on the trunk or extremities, where 2 cm margins are relatively more easily achieved, excision with 2 cm margins should be the standard primary therapy," Dr. Padgett says.

During treatment, she adds, "Communication with the dermatopathologist is critical, as careful histologic review of the excised specimen is necessary to ensure that the entire tumor has been removed."

It’s also important to alert the dermatopathologist than one suspects DM so that the dermatopathologist doesn’t misinterpret any fibrosis observed as evidence of benign proliferation, she says.

"Clinical suspicion is important with any dermal nodule or plaque that is flesh colored to pink in a sun-exposed area on an older individual, particularly a man, possibly with overlying suggestions of a lentigo maligna component," Dr. Padgett says.

Sentinel lymph node (SLN) biopsy represents a useful technique for detecting early metastases to regional lymph nodes, she says. "It has low rates of complications and morbidity when performed by experienced hands. It’s also a useful technique for staging tumors, and may be of prognostic significance in some tumors."

Furthermore, she says physicians routinely perform SLN for melanomas greater than 1 mm in depth. "However, lymph node metastases are much less common in DM than in conventional melanoma," Dr. Padgett says.

Nevertheless, Dr. Padgett says she would consider SLN biopsies for mixed DM’s (but not necessarily for pure DM’s because SLN biopsies have yielded little with regard to these tumors).

"I would consider using radiation therapy as adjuvant treatment if surgical margins were less than 2 cm, or if clear margins could not be achieved," because the tumor was located in a hard-to-treat area, Dr. Padgett says.

"Based on evidence from previous studies, I would consider this when neurotropism was present or if DM were to recur locally," she says.

Dr. Padgett also emphasizes the need for regular follow-up, with skin examinations and lymph node palpation during at a frequency of every two to three months. This is particularly important in the first two years after diagnosis and completion of therapy, which is when 75 percent of local recurrences happen, she says. DT