MAUI, HAWAII Immunohistochemical staining for p75 nerve growth factor receptor is a helpful tool for establishing the diagnosis of desmoplastic melanoma in cases where histopathology is inconclusive and S-100 staining is weak or absent, according to Dr. Maxwell A. Fung. "This stain is one that even a lot of dermatopathlogists have never heard of," he said at the annual Hawaii dermatology seminar sponsored by Skin Disease Education Foundation.
The p75 nerve growth factor receptor is a marker of Schwannian differentiation. It's worth becoming familiar with p75 nerve growth factor receptor because the insurance industry has identified unrecognized desmoplastic melanoma as one of the top-10 causes of malpractice lawsuits involving melanoma, said Dr. Fung of the University of California, Davis.
"S-100 staining is our workhorse, our most sensitive stain for identification of melanomas. But when it's focal or absent, consider p75 nerve growth factor receptor. It's a very sensitive marker for desmoplastic melanoma," said Dr. Fung.
"It's very nonspecificit'll stain a nevus or a neurofibromabut in the context of trying to make a diagnosis of desmoplastic melanoma, if this is positive, it's going to make the diagnosis," he added.
Dr. Fung noted that dermatopath-ologists at Boston University have proposed incorporating p75 nerve growth factor receptor and S-100 staining as a primary immunohistochemical test panel for the diagnosis of desmoplastic melanoma (Am. J. Dermatopathol. 2006;28:1627).
In a separate presentation, Dr. Jeffrey E. Gershenwald raised the possibility that desmoplastic melanoma may in fact not be a melanoma at all.
"There is evolving new genetic data that certainly suggests this may be a different disease. It may actually behave more like a sarcoma," said Dr. Gershenwald of the M.D. Anderson Cancer Center in Houston.
He and his colleagues recently demonstrated how differently desmoplastic melanomas behave in an analysis of the M.D. Anderson database of melanoma patients undergoing wide local excision and sentinel lymph node biopsy.
The investigators divided patients into three subgroups: 1,785 whose melanomas lacked desmoplastic features, 19 with mixed desmoplastic melanoma, and 46 with pure desmoplastic melanoma.
The pure desmoplastic melanomas were significantly thicker and far less likely to be ulcerated than were the nondesmoplastic or mixed desmoplastic melanomas. (See box.)
Moreover, in contrast to the 16%-17% rates of sentinel lymph node positivity in patients with nondesmoplastic or mixed desmoplastic melanoma, the rate of sentinel lymph node involvement in patients with pure desmoplastic melanoma was "almost insignificant," Dr. Gershenwald said. However, the management approach should be the same as for those with all other types of melanoma.
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