Clinical characteristics associated with BRAF, NRAS and KIT mutations in Japanese melanoma patients

Background: The importance of the genetic background of melanoma cells to the individual susceptibility to treatment has become apparent. In Caucasians, BRAF mutations are frequently detected in lesions on the skin of younger patients compared to NRAS and KIT mutations. However, clinical and pathological characteristics associated with BRAF, NRAS and KIT mutations have not been fully evaluated in East Asians.

Objective: To clarify clinical and pathological characteristics associated with BRAF, NRAS and KIT mutations in Japanese melanoma patients.

Methods: Clinical data were retrospectively collected from 11 hospitals in Japan. BRAF, NRAS and KIT mutations were evaluated with polymerase chain reaction and Sanger sequencing. The relationships between these gene mutations and pathological and clinical findings were analyzed.

Results: The number of cases examined was 171 (primary: 135, metastases: 11, paired: 25), and all were Japanese patients. The detection rates of BRAF, NRAS and KIT mutations were 30.4%, 12.3% and 12.9%, respectively. Compared with the wild type, the presence of BRAF mutations was significantly associated with younger age (median, 50.0 years vs. 70.0 years, p<0.001). BRAF mutation was frequently detected in the lesions of the scalp (80%; 4/5), trunk (72.0%; 18/25), extremities (56.7%; 17/30) and neck (44.4%; 4/9), and the least prevalent were the face (22.2%; 2/9), nail (12.5%; 3/24), palm or sole (8.9%; 4/45) and mucosa (0%). NRAS mutations were prevalent in the face (33.3%) and palm or sole (20.0%), and the median age of these patients was 70.5 years. A KIT mutation was observed in the nail apparatus (25%), palm or sole (15.6%) and mucosa (18.2%). The median age of the patients with a KIT mutation was 63.0 years. Heterogeneity of mutations between primary and metastatic lesions was detected in six of 25 cases (24%). Solar elastosis was identified in 12 of 71 cases (15.3%), among which four cases harbored BRAF(V600E) (2 cases), BRAF(V600K), NRAS(Q61K) or NRAS(Q61L), respectively.

Conclusion: Some clinical characteristics associated with BRAF, NRAS and KIT mutations were observed in Japanese patients, and we observed both similarities to and differences from those of Caucasians. Our findings could provide useful information in efforts to clarify the tumor genesis of malignant melanomas.