Survivability in patients with rare sigmoid colon adenocarcinoma variants: exploring the influence of rural–urban continuum codes and social determinants of health in the USA

PURPOSE: This study examined survival outcomes in patients with rare sigmoid colon adenocarcinoma, excluding rectal cancer, with a focus on the combined effects of rural-urban continuum code (RUCC) and median household income (MHI). METHODS: We analyzed the SEER dataset, which includes 93,020 patients diagnosed with this condition. Survival differences were assessed using Kaplan-Meier estimates and multivariable Cox models. Interaction effects between RUCC and MHI were evaluated, and a nomogram was developed to predict five- and 10-year survival probabilities after adjusting for covariates, with sensitivity analyses conducted to assess robustness. RESULTS: A higher degree of rurality was significantly associated with an increased risk of mortality. Patients in RUCC 4 (HR: 1.13; 95% CI: 1.05-1.22) and RUCC 5 (HR: 1.14; 95% CI: 1.06-1.23) had elevated risks compared with RUCC 1. Income modified these associations. Patients in RUCC 2 with MHI above $100,000 had an 8% lower mortality risk (HR: 0.92; 95% CI: 0.83-0.98) than those in RUCC 1 with MHI below $70,000. Similarly, RUCC 4 patients with MHI $90,000-$100,000 experienced a 15% reduction (HR: 0.85; 95% CI: 0.75-0.98). Nomogram predictions indicated the most favorable survival in RUCC 2 with MHI > $100,000 (5 years > 60%; 1 -years ~ 55%), slightly lower survival in RUCC 1 with the same income (5 years 58%; 10 years 52%), and poorest survival in RUCC 4 with MHI < $70,000 (5 years 54%; 10 years 47%), with sensitivity analyses confirming consistent findings. CONCLUSION: Survival outcomes were significantly influenced by both place of residence and socioeconomic status, with the highest survival observed among patients with higher MHI in RUCC 2 and the poorest outcomes among low-income patients in RUCC 4. These results highlight the compounded impact of rurality and socioeconomic disadvantage, underscoring the need for targeted interventions-including strengthened oncology infrastructure, and reduced structural barriers.