Survivability in Patients with Rare Colorectal Adenocarcinoma Variants: Exploring the Influence of Rural-Urban Continuum Codes and Social Determinants of Health in the United States

Purpose Survival disparities in rare sigmoid colon adenocarcinoma are influenced by socioeconomic and geographic factors, particularly rural-urban residence and household income. This study examines the impact of RUCC and median household income (MHI) on survival outcomes, adjusting for clinical and demographic variables. Methods We analyzed data from the SEER database (1998–2017), including 94,697 patients diagnosed with rare histologic subtypes of sigmoid colon adenocarcinoma: signet-ring cell carcinoma (SRCC) and mucinous adenocarcinoma (MAC). Rectal cancer cases were excluded. Kaplan-Meier survival analysis and Cox proportional hazards models were used to assess survival, incorporating RUCC, MHI, age, sex, race, cancer stage, and treatment modalities. Interaction effects between RUCC and MHI were also evaluated. Results Patients residing in rural regions (RUCC 4–5) with low MHI (<$70,000) had the lowest five-year survival probability (0.53, 95% CI: 0.42–0.64), while urban residents (RUCC 1) with high MHI (>$100,000) had the highest survival probability (0.72, 95% CI: 0.58–0.86). Older age, male sex, distant cancer stage, and Black race were significantly associated with increased mortality (p < 0.001). Surgical treatment was strongly associated with improved survival (HR = 0.41, 95% CI: 0.40–0.42, p < 0.001). Chemotherapy also conferred a protective effect in adjusted models (HR = 0.62, 95% CI: 0.61–0.64, p < 0.001). Conclusion Significant geographic and socioeconomic disparities exist in survival outcomes for patients with rare sigmoid colon adenocarcinoma. Targeted public health efforts, including improved access to screening and treatment in rural and low-income areas, are urgently needed to promote equitable cancer care.