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

BACKGROUND

BRAF and NRAS mutation detection is crucial for advanced melanoma treatment. Our aim was to evaluate how different characteristics from formalin-fixed paraffin-embedded (FFPE) samples, age of the block or DNA concentration could influence the success of BRAF and NRAS mutational screening.

METHODS

DNA was obtained from 144 FFPE samples (62 primary melanoma, 43 sentinel lymph nodes [SLN] and 39 metastasis). BRAF and NRAS were sequenced by Sanger sequencing.

RESULTS

Complete sequencing results were obtained from 75% (108/144) of the samples, and at least one gene was sequenced in 89% (128/144) of them. BRAF was mutated in 55% (29/53) and NRAS in 11% (5/45) of the primary melanomas sequenced. DNA concentration correlated with the tumor area used for DNA extraction (mm2) (adj p-value<0.01, r=0.73). The age of the block did not affect sequencing success. In 60% of samples kept for more than 10 years, both BRAF and NRAS were successfully sequenced.

CONCLUSIONS

Preserving sufficient tumor area in FFPE blocks is important. It is necessary to keep the FFPE blocks, no matter their age, as they are necessary to decide the best treatment for the melanoma patient.