Identification of very rare clinically actionable KRAS variants in colorectal cancer patients using a comprehensive large gene panel.

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e15632 Background: While commercially available hotspot testing detects over 99% of the activating mutations in KRAS located at codons 12, 13, 61, and 146, rare oncogenic variants beyond these regions can significantly impact treatment decisions in colorectal cancer (CRC). Herein we showcase the utility of comprehensive gene panel testing in identifying low frequency yet clinically relevant KRAS alterations to enable informed clinical treatment decisions. Methods: 575 CRC specimens were analyzed using CANCERPLEX over a three-year period (KEW, Inc; Cambridge, MA). CANCERPLEX is a comprehensive large gene panel comprising 435 cancer associated genes. A rare KRAS alteration was defined as a variant with a frequency > 0.02% in COSMIC. Variants with clinical actionability in CRC were defined as activating mutations with inferred therapeutic resistance to anti-EGFR antibody therapy. The analytical sensitivity and specificity for single nucleotide polymorphisms (SNPs) in CANCERPLEXwas 99.2% and > 99.9%, respectively. Results: KRAS Q22K, L19F, and G60D were identified as rare oncogenic variants in our analysis of 575 CRC cases. Q22K, L19F, and G60D has been previously reported in 0.009% (7/73000), 0.017% (13/73000), 0.003% (2/73000), respectively, in CRC cases (COSMIC). All three variants have been reported to have transforming potential in vitro and in vivo and trigger activation of downstream oncogenic pathways [PMID:11095964;26284123; 17150185; 20949621]. As activating mutations in KRAS predict lack of response to EGFR antibody therapies, cetuximab and panitumumab were reported as contraindications in all three cases. While not a rare variant, we detected activating mutations in codon 146 in 3% (17/575) of our cohort; strikingly, 5 of the KRAS A146 variants were not identified by prior less comprehensive modes of RAS testing. Conclusions: Low frequency, clinically relevant KRAS variants in CRC may be overlooked using commercially available RAS hotspot assays. In this study we demonstrate that a comprehensive gene panel may detect clinically consequential rare KRAS mutations that may define patients’ treatment and clinical course.