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.