The frequency of rare ALK fusions and their clinical significance in NSCLC.

Abstract

e21012 Background: ALK fusion is one of the key driver mechanisms in non-small cell lung cancer. In some case reports, some rare mutant forms have also been found to be active and drug-susceptible. There are few reports on the detection and verification methods of rare ALK fusions. Here, we counted the rare fusions of ALK detected by NGS and verified them by other methods. Methods: We analyzed 184 patients with NSCLC harboring ALK-rearrangement detected by NGS from January 2020 to January 2022. We counted the rare ALK fusion forms, and selected two of them for verification by RNA sequencing or immunohistochemistry. Results: Of the 184 patients with ALK fusion that we included, 105 were female and 79 were male (medium age 53). Most female were non-smokers except one while nearly 50% male were smokers. EML4-ALK fusion accounted for the highest proportion (170, 92.4%), 5 were ALK fusions with other 5’ partners ( C2orf44, KCNG3, KIF5B, KDM5A, DCTN1), 6 were intergenic region- ALK rearrangements, 2 were fusions without transcription initiation region, and 1 was LOC399815 -ALK and ALK-EML4 double fusion. Rare fusion forms accounted for less than 10%. We further verified two of these rare fusion mutations by RNA sequencing or immunohistochemistry. Interestingly, one of the patients with a KCNG3-exon1- ALK-exon20 fusion detected by DNA sequencing was confirmed to be an EML4-ALK fusion by RNA sequencing, and another patient with an intergenic region- ALK fusion was confirmed positive by immunohistochemistry. Conclusions: The vast majority of ALK fusions are EML4-ALK fusions, but there are a small number of other forms of fusions. DNA sequencing, RNA sequencing and ICH may give different conclusions for ALK fusions, which may be limited by the detection method. For some rare fusion forms, a variety of methods can be used to detect whether it is an active ALK fusion form.