BRAF Mutant Allele Frequency (MAF) Influences Melanoma Clinicopathologic Characteristics

Cutaneous melanoma shows high variability regarding clinicopathological presentation, evolution and prognosis.

Next generation sequencing was performed to analyze hotspot mutations in different areas of primary melanomas (MMp) and their paired metastases. Clinicopathological features were evaluated depending on the degree of variation of the BRAF mutant allele frequency (MAF) in MMp.

In our cohort of 14 superficial spreading, 10 nodular melanomas and 52 metastases, 17/24 (71%) melanomas had a BRAF mutation and 5/24 (21%) had a NRAS mutation. We observed a high variation of BRAF MAF (H-BRAF) in 7/17 (41%) MMp. The H-BRAF MMp were all located on the trunk, had lower Breslow and mitotic indexes and predominantly, a first nodal metastasis. Regions with spindled tumor cells (Spin) and high lymphocytic infiltrate (HInf) were more frequent in the H-BRAF patients (4/7; 57%), whereas regions with epithelial tumor cells (Epit) and low lymphocytic infiltrate (LInf) were predominant (6/10; 60%) and exclusive in the low BRAF MAF variation tumors (L-BRAF). The H-BRAF/Spin/HInf MMp patients had better prognostic features and nodal first metastasis.

The H-BRAF MMp were located on the trunk, had better prognostic characteristics, such as lower Breslow and mitotic indexes as well as high lymphocytic infiltrate.