NRAS Q61R, BRAF V600E immunohistochemistry: A concomitant tool for mutation screening in melanomas

Abstract

Background: The determination of NRAS and BRAF mutation status is a major requirement in the treatment of patients with metastatic melanoma. Mutation specific antibodies against NRASQ61R and BRAFV600E proteins could offer additional data on tumor heterogeneity. The specificity and sensitivity of NRASQ61R immunohistochemistry have recently been reported excellent. We aimed to determine the utility of immunohistochemistry using SP174 anti-NRASQ61R and VE1 anti-BRAFV600E antibodies in the theranostic mutation screening of melanomas. Methods: 142 formalin-fixed paraffin-embedded melanoma samples from 79 patients were analyzed using pyrosequencing and immunohistochemistry. Results: 23 and 26 patients were concluded to have a NRAS-mutated or a BRAF-mutated melanoma respectively. The 23 NRAS Q61R and 23 BRAF V600E-mutant samples with pyrosequencing were all positive in immunohistochemistry with SP174 antibody and VE1 antibody respectively, without any false negative. Proportions and intensities of staining were varied. Other NRAS Q61L , NRAS Q61K , BRAF V600K and BRAF V600R mutants were negative in immunohistochemistry. 6 single cases were immunostained but identified as wild-type using pyrosequencing (1 with SP174 and 5 with VE1). 4/38 patients with multiple samples presented molecular discordant data. Technical limitations are discussed to explain those discrepancies. Anyway we could not rule out real tumor heterogeneity. Conclusions: In our study, we showed that combining immunohistochemistry analysis targeting NRASQ61R and BRAFV600E proteins with molecular analysis was a reliable theranostic tool to face challenging samples of melanoma.