Socioeconomic Determinants of the Use of Molecular Testing in Stage IV Colorectal Cancer

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.

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.

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).

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.