Different progression pattern between acral and nonacral melanoma: A retrospective, comparative, clinicoprognostic study of 492 cases of primary cutaneous melanoma according to tumor site

Background: There are limited data regarding the difference in progression pattern between acral melanoma and nonacral melanoma. Aims: The objectives of this study were to compare the progression pattern between acral and nonacral melanoma and evaluate its impact on clinical outcomes. Methods: Clinical and histopathological features, survival outcomes and prognostic factors of 492 patients with acral melanoma or nonacral melanoma were retrospectively evaluated using the Asan Medical Center database. Results: The male-to-female ratio and the mean age was 1:0.92 and 60.2 years for acral melanoma ( n = 249), and 1:0.85 and 58.4 years for nonacral melanoma ( n = 243), respectively. The demographic difference was not significant. Although prediagnosis duration was longer and the advanced stage was more common in acral melanoma than that in nonacral melanoma, the vertical growth phase was more common in nonacral melanoma than that in acral melanoma, whereas, the horizontal diameter is longer in acral melanoma than that in nonacral melanoma. Dissemination to lymph node was more common in acral melanoma than that in nonacral melanoma. Lymph node involvement was associated with deeper Breslow thickness in nonacral melanoma but not in acral melanoma. The degree of correlation of prediagnosis duration with horizontal diameter was remarkable in acral melanoma, but with Breslow thickness in nonacral melanoma. Overall survival was worse in acral melanoma than that in nonacral melanoma. The prognostic value of Breslow thickness was more remarkable in nonacral melanoma than that in acral melanoma. Limitations: This study is a retrospective, single-center design. Conclusion: Acral melanoma has a longer radial growth phase compared with nonacral melanoma. However, acral melanoma is commonly associated with lymph node dissemination which contributed to worse survival in acral melanoma than nonacral melanoma.