Association between KRAS G13D mutations and anastomotic recurrence in colorectal cancer: Two case reports.

The prevalence of anastomotic recurrence (AR) in colorectal cancer (CRC) after resection of the primary tumor (PT) is 5% to 14%. However, no association has been observed between specific somatic genetic alterations and AR. Such associations may shed light on the mechanism of AR. We experienced 2 patients with AR of CRC. The first patient was a 42-year-old woman who underwent resection of an AR of rectal cancer 2 times within 19 months after resection of the PT. The second patient was a 77-year-old woman who underwent resection of an AR of ascending colon cancer twice within 38 months after resection of the PT. Both cases were diagnosed as repetitive AR. Loss of heterozygosity analysis, microsatellite instability (MSI) study of 9 microsatellite loci, and mutational analysis of KRAS, BRAF, APC, TP53, and SMAD4 were performed. All the lesions, except 1, harbored mutations in APC, KRAS, and TP53, without MSI, after neoadjuvant chemoradiotherapy. The APC, KRAS, and TP53 mutations were pathogenic or likely pathogenic in the PTs and ARs. Both women harbored the same KRAS G13D mutation, which accounts for 8% of all KRAS mutations in sporadic CRC s. The probability of the incidental occurrence of KRAS G13D mutations in both cases is 0.64%, provided that the mutations were independent of AR. Our findings may shed light on the mechanism of AR in CRC, namely, that the PT harbored the same mutations as the AR and the lesions in both cases harbored the KRAS G13D mutation.