NRAS and BRAF mutations in melanoma tumours in relation to clinical characteristics: a study based on mutation screening by pyrosequencing

Abstract

We have previously demonstrated the use of pyrosequencing to investigate NRAS [neuroblastoma RAS viral (v-ras) oncogene homolog] mutations in melanoma biopsies. Here, we expanded the analysis to include BRAF (V-raf murine sarcoma viral oncogene homolog B1), another member of the Ras-Raf-mitogen-activated protein kinase (MAPK) signalling pathway, and analysed a total of 294 melanoma tumours from 219 patients. Mutations in BRAF exons 11 and 15 were identified in 156 (53%) tumours and NRAS exon 2 mutations in 86 (29%) tumours. Overall, mutations in NRAS or BRAF were found in 242 of 294 tumours (82%) and were found to be mutually exclusive in all but two cases (0.7%). Multiple metastases were analysed in 57 of the cases and mutations were identical in all except three, indicating that BRAF and NRAS mutations occur before metastasis. Association with preexisting nevi was significantly higher in BRAF mutated tumours (P=0.014). In addition, tumours with BRAF mutations showed a significantly more frequent moderate to pronounced infiltration of lymphocytes (P=0.013). NRAS mutations were associated with a significantly higher Clark level of invasion (P=0.022) than BRAF mutations. Age at diagnosis was significantly higher in tumours with NRAS mutations than in those with BRAF mutations (P=0.019). NRAS and BRAF mutations, however, did not influence the overall survival from time of diagnosis (P=0.7). In conclusion, the separate genotypes were associated with differences in several key clinical and pathological parameters, indicating differences in the biology of melanoma tumours with different proto-oncogene mutations.

Oncogenic GNAQ mutations are not correlated with disease-free survival in uveal melanoma

“…However, GNAQ mutations have been shown to have similar frequencies at all clinical stages of uveal melanoma progression, and to be independent of chromosomal aberrations, hinting at GNAQ being an early or initiating oncogenic event (Onken et al, 2008). This is consistent with the assumption that frequent oncogenic mutations of BRAF and NRAS in cutaneous melanoma as well as in benign melanocytic nevi (Davies et al, 2002;Pollock et al, 2003), which also activate the MAP-kinase pathway, are early events and are not associated with clinical outcome (Shinozaki et al, 2004;Akslen et al, 2005;Edlundh-Rose et al, 2006).…”

Immunohistochemistry is highly sensitive and specific for the detection of NRASQ61R mutation in melanoma

“…Among RAS mutations, NRASQ61R is the most common in the majority of studies. [11][12][13][14][15] These results have been recently confirmed by a retrospective analysis in a large cohort of patients with advanced melanoma who underwent testing for both BRAF (exon 15) and NRAS (exons 1 and 2) mutations. 5 Finally, it is important to underline that NRASQ61R has been reported to correlate with resistance to BRAF inhibitors in preclinical and clinical data.…”

Testing the divergent pathway hypothesis for melanoma: recent findings and future challenges

“…Since that time, the 1799 T>A transversion in BRAF (V600E) has proven to be the most common somatic mutation in melanoma, accounting for half of all reported mutations [26]. Importantly, the prevalence of BRAF mutations has been shown to differ depending upon the anatomical site of the melanoma, host characteristics (such as nevus density and age) [29][30][31], levels of sun exposure in early life [32,33] and the presence or absence of contiguous neval remnants [34,35]. These observations are consistent with the divergent pathway hypothesis, but the mechanisms through which BRAF mutations arise remain unclear.…”