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

Background: 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.

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.

Results: 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.

Conclusions: 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.