Socioeconomic determinants of the use of molecular testing in stage iv colorectal cancer

OBJECTIVES: Treatment with epidermal growth factor receptor monoclonal antibodies extends life for patients with advanced colorectal cancers (CRCs) whose tumors exhibit wild-type KRAS, but KRAS testing may be underused. We studied the role of socioeconomic factors in the application of KRAS testing.

MATERIALS AND METHODS: We identified subjects with stage IV colorectal adenocarcinoma diagnosed 2010-2015 in the Surveillance, Epidemiology, and End Results (SEER) database. We used multivariable logistic regression models to evaluate associations between clinical/demographic factors and the rate of KRAS testing. We used multivariable-adjusted Cox proportional hazards models to assess survival.

RESULTS: We identified 37,676 patients with stage IV CRC, 31.1% of whom were tested for KRAS mutations, of those who had documented KRAS testing, 44% were KRAS mutant. Patients were more likely to be tested if they were younger (odds ratio [OR]=5.10 for age 20 to 29 vs. 80+, 95% confidence interval [CI]: 3.99-6.54, P<0.01), diagnosed more recently (OR=1.92 for 2015 vs. 2010, 95% CI: 1.77-2.08, P<0.01), or lived in an area of high median household income (OR=1.24 for median household income of >$69,311 vs. <$49,265, 95% CI: 1.14-1.35, P<0.01). Patients were less likely to be tested if they had Medicaid (OR=0.83, 95% CI: 0.77-0.88, P<0.01) or were unmarried (OR=0.78, 95% CI: 0.75-0.82, P<0.0001). The risk of death was decreased in patients who received KRAS testing (hazard ratio=0.77, 95% CI: 0.75-0.80, P<0.01).

CONCLUSIONS: We found a low rate of KRAS testing in CRC patients with those living in low-income areas less likely to be tested, even after controlling for Medicaid insurance. Our study suggests that socioeconomic disparities persist despite Medicaid insurance.