Mutational status of naevus-associated melanomas

Abstract

Introduction Melanoma origin has always been a debated subject, as well as the role of adjacent melanocytic nevi. Epidemiological and histopathological studies point to melanomas arising either de novo or from a nevus. Methods Sixty-one melanomas found in association with a preexisting nevus were microdissected, after careful selection of cell subpopulations and submitted to Sanger sequencing of the BRAF, NRAS, C-KIT, PPP6C, STK19 and RAC1 genes. Each gene was evaluated twice in all samples by sequencing or by sequencing and another confirmation method, allele-specific fluorescent polymerase chain reaction (PCR) and capillary electrophoresis detection, or by SNaPshot Analysis. Only mutations confirmed via two different molecular methods or twice by sequencing were considered positive. Results The majority of cases presented concordance of mutational status between melanoma and the associated nevus for all 6 genes (40/60; 66.7%). Nine cases presented concomitant BRAF and NRAS mutations, including one case, in which both the melanoma and the adjacent nevus harbored V600E and Q61K double mutations. In two cases, both melanoma and associated nevus, located on acral sites were BRAF mutated, including an acral lentiginous melanoma. Conclusions This is the largest nevus-associated melanoma series molecularly evaluated to our knowledge. The majority of melanomas and adjacent nevi in our sample share the same mutational profile, corroborating the theory that the adjacent nevus and melanoma are clonally related and that melanoma originated within a nevus.

Time and tumor type (primary or metastatic) do not influence the detection of BRAF/NRAS mutations in formalin fixed paraffin embedded samples from melanomas

“…This evidence has already been reported [16]. As previously observed [15,[17][18][19], in some samples we have detected co-occurrence of BRAF and NRAS mutations. At the single cell level, mutations in BRAF or NRAS are mutually exclusive [17].…”

“…The frequency of genomic mutations detected in primary tumors correlated with that previously reported [4,15]. Shitara et al showed that laser microdissection does not alter the frequency of BRAF and NRAS mutations [15]. We observed discordances between mutations found in the primary melanoma and the SLN and/or the metastasis in some cases.…”

Melanocytic nevi and melanoma: unraveling a complex relationship

“…Genetic analyses of such histologically contiguous benign nevus-melanoma pairs support the hypothesis that the melanoma cells were derived directly from the nevus cells. 31,68–72 Although cases of driver mutation (that is, RAF/RAS ) discordance between paired nevus and melanoma have been reported 70,73 and are interesting mechanistically, these cases appear to be much less common and some may represent coincidental collision lesions between unrelated nevi and melanomas.…”

Discrepant mutational status between naevi and melanomas in naevus-associated melanomas: about mutation-specific immunohistochemistry

“…A major advantage of this highly sensitive and specific immunohistochemistry is to allow an in situ interpretation without requiring the sometimes challenging isolation of naevus, melanoma and nontumour cells. Molecular false negative results are reported in some challenging melanoma samples and could explain some of the discrepant mutational results reported by Shitara et al . Nevertheless, mutation‐specific immunohistochemistry is to date not available for the NRAS Q61K mutant encountered by Shitara et al .…”

“…recently reported on BRAF and NRAS mutational status in a large series of 61 naevus‐associated melanomas . DNA analyses performed in microdissected naevus and melanoma areas concluded that there were 36 BRAF V600E and 13 NRAS Q61K mutated cases (no other BRAF V600 or NRAS Q61 mutations), with discrepant mutational status between naevi and melanomas in 13 and nine cases, respectively . This high rate of discrepancy requires further consideration.…”