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KIT aberrations observed in some amelanotic acral melanomas

Amelanotic acral melanomas were difficult to diagnose clinically and histopathologically, with BRAF mutations rare and some KIT aberrations detected, according to recent study results.

Researchers assessed 35 South Korean patients with amelanotic acral melanoma (AAM; mean age, 66.8 years; 68.6% men), including 28 cases of complete-type and seven cases of incomplete-type AAM. Clinicopathological features, BRAF mutations and KIT aberrations were analyzed.

Twenty-six patients developed AAMs on the foot (74.3%), and nine patients developed AAMs on the hand (25.7%). Sixteen cases, divided evenly between the foot and hand, included subungal involvement (45.7%). Ulceration was observed in 29 AAMs (82.9%). Histopathological review of skin biopsy slides was conducted for 33 patients (nodular melanoma, 63.6%; acral lentiginous melanoma, 36.4%). Epitheloid and spindled were the most frequent cell types affected.

HMB-45 staining was strongly positive in 66.7% of 33 AAMs; four (12.1%) were negative, including three that were complete.

DNA sequencing detected BRAF V600E mutation in two patients (6.06%), one complete-type and one incomplete-type AAM. Of KIT aberrations in 11 patients (33.3%), nine were complete-type and two incomplete-type AAMs. C-kit staining showed a weak correlation with KIT aberrations. Tumor-node-metastasis stage I or II was present in 20 patients; mean survival was 30.14 ± 4.54 months for the entire cohort.

“Our data reveal that AAMs are difficult to diagnose clinically and histopathologically; HMB-45 staining was sometimes negative in AAMs ... ,” the researchers concluded, noting that the study was limited by its size. “We expect that tyrosine kinase inhibitors would be effective for KIT-mutated patients with complete-type AAMs. Physicians should be aware of the rare occurrence of AAMs, and further study is needed to correctly understand and characterize AAMs.”

Disclosure: The researchers report no relevant financial disclosures.