Desmoplastic melanoma: A pathologically and clinically distinct form of cutaneous melanoma

Background: Desmoplastic melanoma (DM) is a rare variant characterized by the presence of fusiform melanocytes in a sclerotic stroma. Pathologic heterogeneity within DM may account for the controversy regarding the clinical presentation and prognosis of DM compared with conventional melanoma (CM). Methods: We identified 131 patients with a diagnosis of DM seen between 1979 and 2002. Tumors were categorized as either pure DM (pDM; n = 92), if desmoplasia was prominent throughout the entire invasive tumor, or mixed DM (mDM; n = 39), if fibrosis was well developed in only parts of an otherwise non-DM. Differences in clinical behavior among pDM, mDM, and CM (n = 3976) were examined. Results: Seventy-three percent of patients with DM had tumors >2 mm in depth, compared with 31% of patients with CM (P < .001). Regional nodal metastasis was uncommon in patients who presented with clinically localized pDM (1%) compared with those with mDM (10%) or CM (6%) (P < .05, pDM vs. CM). Five-year melanoma-specific mortality was lower for patients who presented with pDM compared with mDM (11% vs. 31%; P < .01). Patients with pDM and CM had a similar melanoma-specific mortality despite a 3-fold difference in median tumor depth (3.6 vs. 1.2 mm, respectively). Conclusions: DMs can be divided into two subtypes based on a histological quantification of desmoplasia. Tumors with prominent fibrosis (pure subtype) are unlikely to disseminate to regional lymph nodes and are associated with a favorable outcome when compared with those with mixed desmoplasia or CM.