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Xiang Gao, Amanda R. Kahl, Paolo Goffredo, Albert Y. Lin, Praveen Vikas, Imran Hassan, and Mary E. Charlton

Background: National guidelines recommend chemotherapy as the mainstay of treatment for stage IV colon cancer, with primary tumor resection (PTR) reserved for patients with symptomatic primary or curable disease. The aims of this study were to characterize the treatment modalities received by patients with stage IV colon cancer and to determine the patient-, tumor-, and hospital-level factors associated with those treatments. Methods: Patients diagnosed with stage IV colon cancer in 2014 were extracted from the SEER Patterns of Care initiative. Treatments were categorized into chemotherapy only, PTR only, PTR + chemotherapy, and none/unknown. Results: The total weighted number of cases was 3,336; 17% of patients received PTR only, 23% received chemotherapy only, 41% received PTR + chemotherapy, and 17% received no treatment. In multivariable analyses, compared with chemotherapy only, PTR + chemotherapy was associated with being married (odds ratio [OR], 1.9), having bowel obstruction (OR, 2.55), and having perforation (OR, 2.29), whereas older age (OR, 5.95), Medicaid coverage (OR, 2.46), higher T stage (OR, 3.51), and higher N stage (OR, 6.77) were associated with PTR only. Patients who received no treatment did not have more comorbidities or more severe disease burden but were more likely to be older (OR, 3.91) and non-Hispanic African American (OR, 2.92; all P<.05). Treatment at smaller, nonacademic hospitals was associated with PTR (± chemotherapy). Conclusions: PTR was included in the treatment regimen for most patients with stage IV colon cancer and was associated with smaller, nonacademic hospitals. Efforts to improve guideline implementation may be beneficial in these hospitals and also in non-Hispanic African American and older populations.

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Mary E. Charlton, Amanda R. Kahl, Alissa A. Greenbaum, Jordan J. Karlitz, Chi Lin, Charles F. Lynch, and Vivien W. Chen

Purpose: KRAS mutations and tumor location have been associated with response to targeted therapy among patients with stage IV colorectal cancer (CRC) in various trials. This study performed the first population-based examination of associations between KRAS mutations, tumor location, and survival, and assessed factors associated with documented KRAS testing. Methods: Patients with stage IV adenocarcinoma of the colon/rectum diagnosed from 2010 to 2013 were extracted from SEER data. Analyses of patient characteristics, KRAS testing, and tumor location were conducted using logistic regression. Cox proportional hazards models assessed relationships between KRAS mutations, tumor location, and risk of all-cause death. Results: Of 22,542 patients, 30% received KRAS testing, and 44% of these had mutations. Those tested tended to be younger, married, and metropolitan area residents, and have private insurance or Medicare. Rates of KRAS testing also varied by registry (range, 20%–46%). Patients with right-sided colon cancer (vs left-sided) tended to be older, female, and black; have mucinous, KRAS-mutant tumors; and have a greater risk of death (hazard ratio [HR], 1.27; 95% CI, 1.22–1.32). KRAS mutations were not associated with greater risk of death in the overall population; however, they were associated with greater risk of death among patients with left-sided colon cancer (HR, 1.19; 95% CI, 1.05–1.33). Conclusions: This large population-based study showed that among patients initially diagnosed with stage IV CRC, right-sided colon cancer was associated with greater risk of death compared with left-sided cancer, and KRAS mutations were only associated with risk of death in left-sided colon cancer. An unexpected finding was that among patients with stage IV disease, right-sided cancer was more commonly seen in black patients versus whites. Future studies should further explore these associations and determine the role of biology versus treatment differences. In addition, use of KRAS testing is increasing, but there is wide geographic variation wherein disparities related to insurance coverage and rurality may warrant further study.