Background: Tumor location and KRAS mutational status have emerged as prognostic factors of colorectal cancer. We aimed to define the prognostic impact of primary tumor location and KRAS mutational status among synchronous colorectal liver metastases (CRLM) patients who underwent simultaneous curative-intent surgery (SCIS). Methods: We compared the clinicopathologic characteristics and long-term outcomes of 227 patients who underwent SCIS for synchronous CRLM, according to tumor location and KRAS mutational status. We cross-classified tumor location and KRAS mutational status and compared survival outcomes between the four resulting patient groups. Results: Forty-one patients (18.1%) had right-sided (RS) tumors and 186 (81.9%) had left-sided (LS) tumors. One-third of tumors (78/227) harbored KRAS mutations. The KRAS mutant-type (KRAS-mt) was more commonly observed among RS tumors than among LS tumors [21/41 (51.2%) vs. 57/186 (30.6%), p = 0.012]. Median follow-up time was 43.4 months. Patients with RS tumors had shorter survival times than those with LS tumors [median disease-free survival (DFS): RS, 9.9 months vs. LS, 12.1 months, p = 0.003; median overall survival (OS): RS, 49.7 months vs. LS, 88.8 months, p = 0.039]. RS tumors were a negative prognostic factor for DFS [hazard ratio (HR) 1.878, p = 0.001] and OS (HR 1.660, p = 0.060). RS KRAS-mt and LS KRAS wild-type (KRAS-wt) tumors had the worst and best oncological outcomes, respectively. Conclusion: Tumor location has a prognostic impact in patients who underwent SCIS for CRLM, and RS KRAS-mt tumors yielded the worst oncological outcome. These results may allow for more tailored multimodality treatments.
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