Recognizing DM: Desmoplastic melanoma frequently misdiagnosed

Key Points

Charlottesville, Va. - Although desmoplastic melanoma (DM) represents less than 2 percent of all melanomas, dermatologists should know how to recognize and treat it, because it's often misdiagnosed both clinically and histologically, an expert says.

Furthermore, she says that although researchers first recognized this condition's fibrotic component in 1971 and later expanded the definition to include melanomas with a neuroid appearance, "Today, we recognize the desmoplastic melanomas and the desmoplastic neurotrophic melanomas as part of a clinical and histologic continuum that shares many different features."

Histology

Histologic diagnosis is not always straightforward, either, she adds. "The presence of fibrosis within the tumor can resemble benign processes, such as a scar or sclerosing nevus," she says. Classically, she adds, the histology of DM reveals spindle-shaped, non-pigmented cells located throughout the dermis, with varying degrees of nuclear atypia and possibly small numbers of mitotic features.

Dermatoscopically, she says when pigmentation is absent, "The classic features of melanoma that we look for are not frequently seen. Instead, abnormal vascular features such as linear vessels, milky red areas or scar-like areas that reflect fibrosis may be helpful dermatoscopic findings (Debarbieux S, Ronger-Salve S, Dalle S et al. Br J Dermatol. 2008 Aug;159(2):360-3. Epub 2008 Jun 28)."

She says, "Neurotropism is seen in certain DMs as infiltration of the nerves by the tumor cells themselves, or the tumor cells themselves may form neural-like structures."

Due to its lack of distinguishing clinical presentation, Dr. Padgett says, "DM is rarely diagnosed at an early stage." At diagnosis, she says most DMs are greater than 1 mm in depth, and many are greater than 4 mm. "The majority are Clark's level four or five, reflecting a large and deep degree of invasion into the reticular dermis and subcutis." Ulceration occurs in 20 percent of cases, and neurotropism in 40 percent, she adds.

"Local recurrence is a hallmark and very frequent feature of DM. This may present as a dermal or subcutaneous mass in the area of the primary tumor." Following complete excision, she adds, local recurrence rates as high as 40 percent to 60 percent have been reported. "Clark's level, presence of neurotropism, and head and neck location have been independently identified as predictors of local recurrence. And of the DMs that recur locally, three-fourths will do so within the initial two years of diagnosis and therapy." Unfortunately, she adds, local recurrence also is associated with increased risk of metastatic disease. "When distant metastasis occurs, it happens most frequently to the lung - up to 80 percent in one case series."