Pure desmoplastic melanoma: A melanoma with distinctive clinical behavior

Objective: The purpose of the study was to evaluate the excision margin necessary for desmoplastic melanoma (DM). Background: DM consists of 2 histologic subtypes, pure DM (PDM) and mixed DM (MDM), differing in extent of fibrotic component. We investigated clinical and therapeutic determinants of prognosis in these DM entities. Methods: We reviewed 118 PDM and 124 MDM treated at our Institute over 25 years. Local relapse, distant metastasis, and survival were studied. Results: Most (91.7%) distant metastases in PDM developed after 1 or more local recurrences; whereas distant metastasis usually (79.6%) occurred as first event in MDM. Overall mortality trends in relation to lesion-thickness-plus-excision-width differed for PDM (P = 0.014) but not MDM (P = 0.185). For PDM, 5-year crude cumulative incidence (CCI) of mortality was higher (40.0%) for thin tumors (≤2 mm thick) excised with 1 cm margin than those excised with 2 cm (14.8%); CCI of mortality for PDM >2 mm thick excised with 2 cm margins (13.4%) was similar to that for thin PDM lesions excised with 2 cm (14.8%). CCI of local recurrence was also greater in PDM excised with 1 cm margins. In MDM, mortality increased with stage but was independent of excision width (CCI: 29.4% for ≤2 mm/2 cm, 31.3% for ≤2 mm/1 cm, and 48.3% for >2 mm/2 cm); a similar trend was found for MDM distant metastases. Conclusions: In PDM, limited excision width is associated with significantly greater local recurrence and mortality; treatment should be excision with 2 cm margins even for thin lesions. MDM behaves similarly to other melanomas; treatment should follow guidelines on melanoma management.