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Pathology:
doi: 10.1097/PAT.0000000000000077
Anatomical Pathology

Concordant BRAFV600E mutation status in primary melanomas and associated naevi: implications for mutation testing of primary melanomas

Kakavand, Hojabr1,2; Crainic, Oana3,4; Lum, Trina3; O’Toole, Sandra A.1,3,5; Kefford, Richard F.1,2; Thompson, John F.1,2,6; Wilmott, James S.2; Long, Georgina V.1,2; Scolyer, Richard A.1,2,3

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Abstract

Summary

There is concern that BRAF mutant naevus cells admixed with melanoma cells could cause false positive mutation tests in BRAF wild-type melanomas. We sought to assess the frequency of BRAFV600E mutations in primary melanomas arising with/without associated naevi and determine BRAFV600E concordance between melanomas and associated naevi.

Formalin fixed, paraffin embedded (FFPE) tissue from 57 patients with primary melanomas with/without associated naevi was immunohistochemically stained to detect BRAFV600E mutation. In a subset of patients (n = 29), molecular mutation testing was also carried out using a panel of 238 known genetic variants.

Of the primary melanomas with an associated naevus (n = 29), 55% were BRAFV600E mutant with 100% concordance between the melanoma and associated naevus. In contrast, only 21% of the primary melanomas unassociated with naevi were BRAFV600E mutant (p = 0.009).

Our results suggest that melanomas with associated naevi have a higher frequency of BRAFV600E mutations than melanomas unassociated with naevi. Furthermore, melanomas and their associated naevi were concordant in BRAFV600E status, which suggests that false positive mutation tests occurring as a consequence of admixed BRAF mutant naevus cells in BRAF wild-type primary melanomas are unlikely to be a problem in clinical practice. The findings have important implications for adjuvant clinical trials of targeted therapies.

© 2014 Royal College of pathologists of Australasia

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