Clinicopathological and molecular features of genome-stable colorectal cancers

Colorectal cancers (CRCs) are traditionally divided into those with either chromosomal instability (CIN) or microsatellite instability (MSI). By utilizing TCGA data, the Laird team found a subset of CRCs, namely, genome-stable CRCs (GS CRCs), which lack both CIN and MSI. Although the molecular features of GS CRCs have been described in detail, the clinicopathological features are not well defined. A total of 437 CRCs were analyzed for copy number variation (CNV) statuses in eight genes (ARID1A, EGFR, FGFR1, KDM5B, MYBL2, MYC, SALL4, and SETDB1) using droplet-digital PCR. CRCs that showed CNV in <= one gene and no MSI were defined as GS-like CRCs. Clinicopathological and molecular features of GS-like CRCs were compared with those of CIN-like CRCs. GS-like CRCs comprised 4.6% of CRCs and showed a predilection toward the proximal colon, lower nuclear optical density, KRAS mutation, PIK3CA mutation, and aberrant expression of KRT7. Survival analysis showed no significant difference between the three subgroups. Through our study, the GS-like subtype was found to comprise a minor proportion of CRCs and have proclivity toward a proximal bowel location, hypochromatic tumor nuclei, aberrant KRT7 expression, and a high frequency of KRAS and PIK3CA mutations.