A case-control study of desmoplastic melanoma

Abstract

7529 Background: Previous studies have established that patients with desmoplastic melanoma have thicker primary tumors. Consequently, comparisons between desmoplastic melanoma and other forms of melanoma in these studies have been strongly biased by differences in Breslow stage. This is the first case-matched control study comparing desmoplastic melanoma with other forms of melanoma. Methods: From a database of 3202 melanoma patients treated at one institution, 89 patients with desmoplastic melanoma and 178 case-matched control patients (2:1) were identified by matching for thickness, age, gender, and year of diagnosis. Clinical, pathological, and outcome information were analyzed. Results: The median tumor thickness for all patients in the database is 0.96 mm, whereas the median thickness for desmoplastic melanoma patients is 2.60 mm. As per study design, the median tumor thickness for the 178 case-matched control patients is the same (2.60 mm) as for desmoplastic melanoma patients. Presentation with AJCC stage III or IV disease is less common in desmoplastic melanoma patients compared to case-matched control patients (5% versus 21%, p < 0.001). Re-excisions to obtain clear surgical margins are required more often in desmoplastic melanoma (21% versus 6%; p < 0.001). The risk of positive sentinel nodes is lower in desmoplastic melanoma patients compared to case-matched control patients (8% versus 34%, p = 0.013). Overall survival, cause-specific survival, and disease-free survival in desmoplastic melanoma patients are the same as those in case-matched control patients. Conclusions: Desmoplastic melanoma patients present with thicker primary melanomas than patients with other forms of melanoma. Use of case-matched control patients matched for tumor thickness avoids biases introduced by this observation. Desmoplastic melanomas are more locally aggressive, but have a lower risk of lymph node metastases compared to melanomas in case-matched control patients. The observed 8% rate of positive sentinel nodes in desmoplastic melanoma patients should be factored into decisions concerning sentinel lymph node biopsy. Importantly, desmoplastic melanoma patients have survival rates similar to patients with other melanomas of similar thickness. No significant financial relationships to disclose.