Metastatic Melanoma with Adil Daud, MD and Boris C. Bastian, MD, PhD - Episode 1
How frequently are BRAF alterations missed that are subsequently picked up using a different test?
First of all, there are different types of BRAF alterations that can cause melanoma. So there are mutations. Most of them occur in exon 15 of BRAF. The most frequently mutated codon is 600 and the most frequent prevalent mutation is a V600E. That can actually rise through two types of nucleotide changes, a single and a dinucleotide change, and those account for about 70% of all V600 mutations. So there are additional substitutions. V600K is the most frequent but there are even others that are clearly pathogenic and cause melanoma. Then there are mutations in the immediate vicinity of V600, 601, and 597.
On top of these mutations that can activate BRAF, there are genetic rearrangements of the BRAF gene where there are actually no mutations but the BRAF kinase domain is put behind some other gene. Depending on which BRAF alteration one would like to pick up, one has to pick the right tests. The current FDA-approved tests, like the cobas and the bioMérieux test, really are very distinctly focusing on V600. The cobas test has low sensitivity for non-V600E mutations and the V600E mutations that are caused by dinucleotide mutations. In the literature, the sensitivity for picking up mutations of V600 are about 80%. If the test is actually negative and there is clearly a rationale for using another test, you can really make sure that there is no actionable BRAF mutation.
The bioMérieux test is more sensitive in terms of better detecting V600K but it will also miss any of the other mutations, and specifically none of these tests will detect any of the structural rearrangements of BRAF fusions. In my view, particularly if the result is negative, it’s important to consider those technical limitations of the assay and consider other tests to really confirm that the patient is negative.
CASE: Metastatic Melanoma
Michelle is a 55-year old who was referred by her primary care physician to receive a biopsy for a suspicious mole during a routine visit. Results of the biopsy and other subsequent tests revealed that she had an M1b stage tumor (lung metastasis and a less than ULN LDH level). Her ECOG PS is 0.
She was referred from the community setting to a tertiary center, at which point a second test was conducted using the bioMérieux HxID-BRAF kit. This assay was positive for the BRAF V600K mutation