Abstract
ABSTRACTBackgroundNTRK fusions are emerging tissue-agnostic drug targets in malignancies including colorectal cancers (CRCs), but their detailed landscape in the context of various colorectal carcinogenesis pathways remains to be investigated.MethodsPan-TRK expression was assessed by immunohistochemistry in retrospectively collected colorectal epithelial tumor tissues, including 441 CRCs (133 microsatellite instability-high (MSI-high) and 308 microsatellite stable (MSS)) and 565 premalignant colorectal lesions (300 serrated lesions and 265 conventional adenomas). TRK-positive cases were subjected to next-generation sequencing and/or fluorescence in situ hybridization to confirm NTRK rearrangements.ResultsTRK positivity was not observed in any of the MSS CRCs, conventional adenomas, traditional serrated adenomas, or hyperplastic polyps, whereas TRK positivity was observed in 11 of 58 (19%) sporadic MSI-high CRCs, 4 of 23 (17%) sessile serrated lesions with dysplasia (SSLDs), and 5 of 132 (4%) SSLs. The 11 TRK-positive MSI-high CRCs commonly harbored CpG island methylator phenotype-high (CIMP-high), MLH1 methylation, KRAS/BRAF wild-type, and NTRK1 or NTRK3 fusion (TPM3-NTRK1, TPR-NTRK1, LMNA-NTRK1, SFPQ-NTRK1, ETV6-NTRK3, or EML4-NTRK3). Both NTRK1 or NTRK3 rearrangement and KRAS/BRAF wild-type were detected in all nine TRK-positive SSL(D)s, seven of which demonstrated MSS and/or CIMP-low. TRK overexpression and early dysplastic changes are occasionally co-localized in the crypt base area of SSLs. Age-related occurrence patterns suggest that the progression interval from NTRK-rearranged SSLs to CRCs may be shorter than from BRAF-mutated SSLs to CRCs.ConclusionNTRK-rearranged colorectal tumors develop exclusively through the serrated neoplasia pathway and can be initiated from non-dysplastic SSLs without KRAS/BRAF mutations prior to full occurrence of MSI-high/CIMP-high.
Publisher
Cold Spring Harbor Laboratory