BRAF-V600 Mutation Heterogeneity in Primary and Metastatic Melanoma: A Study With Pyrosequencing and Immunohistochemistry.

The BRAF-V600 mutation is the most common mutation in cutaneous melanomas and is currently considered a target mutation when planning treatment for metastatic melanoma patients. Various techniques are used to determine the mutation status. The aim of this study was to determine the BRAF-V600 mutation status in primary and metastatic foci of melanoma cases and the consistency between the results of immunohistochemical and molecular methods.A total of 48 primary or metastatic cases were included in the study. Pyrosequencing was used as the molecular method and the VE1 antibody for immunohistochemical evaluation when determining the BRAF-V600 mutation.The BRAF-V600 mutation was found in 75 of the 96 tumors (78.1%) from the 48 cases. V600E and V600K were present in 60 and 10 tumors, respectively, whereas V600R and V600M were present in 2 tumors and V600G in 1 tumor. There was no mutation in 5 metastases (12.8%) of the 39 cases with a V600 mutation in the primary tumor and no mutation in the primary tumor of 2 of the 36 cases (5.6%) with the V600 mutation in the metastasis. Fifty-six tumors were immunohistochemically positive where a V600E mutation was detected with pyrosequencing. Wild-type tumors (n = 20) and tumors with non-V600E mutations (n = 15) on pyrosequencing were immunonegative with VE1. The sensitivity and specificity of immunohistochemistry were 93.3% and 97.2%, respectively.In conclusion, BRAF-V600 mutation inconsistencies of up to 14.5% can be seen between the primary and metastatic foci in melanoma cases. These findings should be taken into account when planning targeted therapy and deciding on treatment responsiveness/unresponsiveness. An immunohistochemical method can be used as the first step to detect a BRAF-V600 mutation but additional molecular methods should be used when immunohistochemistry results are negative.