Amelanotic acral melanomas: clinicopathological, BRAF mutation, and KIT aberration analyses

Background: Amelanotic acral melanoma (AAM) is very rare and difficult to diagnose both clinically and pathologically. Complete-type AAM shows no black to brown pigmentation in the lesion, whereas incomplete-type AAM shows focal or subtle pigmentation. AAM has been the subject of few investigations.

Objectives: We analyzed the clinicopathological features, BRAF mutations, and KIT aberrations in 35 Korean AAM cases.

Methods: We included 28 cases of complete-type and 7 cases of incomplete-type AAM.

Results: In all, 26 AAMs (45.7%) were located on the feet of patients, 21 of which (82.9%) showed ulceration. Sixteen cases developed in subungual areas. Nodular melanoma was the most common histopathological subtype (63.6%). The most frequent cell types affected were epithelioid and spindled. HMB-45 staining was strongly positive in 66.7% of AAMs; 4 (12.1%) were negative for HMB-45, and 3 of these were complete-type AAMs. Of 33 total patients, BRAF mutations were detected in 2 AAM cases, and KIT aberrations were present in 11 cases (33.3%). Four cases (12.1%), all of which were complete-type AAMs, had KIT mutations. KIT aberrations were weakly correlated with c-kit staining. Twenty patients were TNM stage I or II, and mean survival was 30.14 ± 4.54 months.

Limitations: The study is limited by the small number of patients.

Conclusion: Physicians should be aware of rare and hard-to-diagnose AAMs. We expect that tyrosine kinase inhibitors would be effective for KIT-mutated patients with complete-type AAMs.