Abstract
Desmoplastic Melanoma (DM) comprises only 1-4% of all primary cutaneous melanoma, making it a rare subtype of melanoma.1 It often presents as amelanotic firm papule or nodule.2,3
We present a 76-year-old White male with history of NMSC status post excision who initially presented for pruritic lesion on his nose, found to have a 0.9 cm pink papulonodule located on the left medial scapular back a pearly pink papule on his left medial scapular bag (Figure 1).
A shave biopsy was performed with several histopathologic reads. The pathology demonstrated expansile proliferation of hyperchromatic spindle-shaped cells associated with a collagenous stromal response. Immunohistochemical displays diffuse positive tumor staining for S-100 protein and SOX-10 without staining evidence for Melan-A, Mit-f, CD34 or Factor XIIa. Hypercellular areas demonstrated up to 5 mitoses per HPF. The differential included malignant peripheral nerve sheath tumor arising within a neurofibroma or amelanotic malignant melanoma with spindled and desmoplastic features. On repeat excisional biopsy, immunohistochemistry was positive for SOX-10, S-100, and PRAME and focally positive for Melan-A and negative for desmin. Findings were most consistent with desmoplastic melanoma. Lymph node biopsies were negative. Patient was scheduled for excision without recurrence.
Unfortunately, DM is often diagnosed at later stages due to its unremarkable clinical appearance.1 Therefore, it is important that dermatologists are trained to adequately recognize key features of these rare subtypes of malignant melanomas. It is also critical to perform frequent and thorough skin exams on patients at increased risk of developing Malignant Melanoma.