Racial disparities and prognostic factors in cancer-specific survival for patients with metastatic rectal cancer.

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e15674 Background: Significant advances in early diagnosis and treatment have improved cancer-specific survival rates for rectal cancer. However, these gains have not been equitably distributed across all racial and ethnic groups, with minorities experiencing worse outcomes compared to non-minorities. Despite increasing awareness of racial disparities in oncology, research specifically examining disparities in cancer-specific survival (CSS) among patients with metastatic rectal cancer remains limited. This study seeks to address this gap by investigating racial disparities in survival outcomes and its associated prognostic factors. Methods: We evaluated patients ≥18 years of age with rectal cancer from the Surveillance, Epidemiology, and End Results (SEER) database, with a study period from 2018 to 2021. SEER has collected information regarding MSI status since 2018, hence, our study period. The study population included adult patients diagnosed with rectal cancer as first primary, histologically confirmed diagnoses, complete data on MSI status, metastatic diagnosis, and known cause of death. A retrospective cohort study was done. Categorical variables were described as frequencies and percentages and compared using chi-squared test. Univariate and multivariate Cox regression models were used to assess the association between the exposure variables and CSS. Results: We included 3,095 individuals with metastatic rectal cancer (mRC). The majority were non-Hispanic White (NHW) (65.82%), followed by Hispanic (H) (15.15%), Asian/Pacific Islander (API) (10.11%), Non-Hispanic Black (NHB) (8.17%), and American Indian/Alaskan Native (AIAN) (0.74%). Most patients were male (63.10%), with 36.90% female. Young-onset metastatic rectal cancer (YO-mRC) counted for 23.72% of cases, while average-onset metastatic rectal cancer (AO-mRC) comprised 76.28%. NHB individuals had a significantly higher risk of mortality compared to NHW individuals (HR: 1.29, 95% CI: 1.05–1.60, p=0.015). Patients with AO-mRC demonstrated worse survival compared to those with YO-mRC (HR: 1.30, 95% CI: 1.12–1.50, p=0.001). MSI-high tumors were associated with significantly lower mortality risk compared to MSI-stable tumors (HR: 0.57, 95% CI: 0.37–0.87, p=0.01). The presence of bone metastases (HR: 2.15), brain metastases (HR: 2.27), and liver metastases (HR: 1.40) significantly increased mortality risk (all p<0.001). Conclusions: We found significant racial disparities in cancer-specific survival among Black patients with mRC, who have a 29% higher risk of death compared to non-Hispanic White patients. YO-mRC is associated with better survival compared to AO-mRC, possibly reflecting improved treatment tolerance in younger populations. Additionally, the lower risk of death observed in patients with MSI-high tumors reinforces the prognostic importance of MSI status in mRC. Racial disparities and prognostic factors in cancer-specific survival for patients with metastatic rectal cancer. Variable Unadjusted HR (95% CI) p value Adjusted HR (95% CI) p value Race Non-Hispanic White Ref. Hispanic 1.03 (0.87-1.22) 0.697 1.05 (0.88-1.25) 0.536 Non-Hispanic Black 1.38 (1.12-1.70) 0.002 1.29 (1.05-1.60) 0.015 Non-Hispanic Asian/PI 0.83 (0.67-1.03) 0.102 0.86 (0.69-1.07) 0.194 Non-Hispanic AI 1.17 (0.62-2.18) 0.617 1.14 (0.61-2.15) 0.666 Onset Young-Onset Ref. Average-Onset 1.45 (1.25-1.68) <0.001 1.30 (1.12-1.50) 0.001 ☨ Sex Male Ref. Female 0.92 (0.81-1.04) 0.188 0.91 (0.81-1.04) 0.184 Socioeconomic Status <$40,000 Ref. $40,000-$79,999 1.08 (0.69-1.69) 0.72 *Not included due to collinearity $80,000-$100,000 0.99 (0.63-1.55) 0.969 >$100,000 0.89 (0.56-1.40) 0.62 Area of Living Non-Metropolitan Ref. Metropolitan 0.97 (0.81-1.15) 0.734 1.04 (0.87-1.24) 0.657 MSI status MSI stable Ref. MSI low 1.17 (0.81-1.69) 0.391 1.13 (0.78-1.64) 0.511 MSI high 0.65 (0.43-0.99) 0.045 0.57 (0.37-0.87) 0.01 ☨ Bone Metastases 2.59 (2.16-3.10) <0.001 2.15 (1.79-2.59) <0.001 ☨ Brain Metastases 2.98 (2.07-4.29) <0.001 2.27 (1.56-3.30) <0.001 ☨ Lung Metastases 1.35 (1.20-1.52) <0.001 1.10 (0.97-1.24) 0.126 Liver Metastases 1.38 (1.20-1.58) <0.001 1.40 (1.21-1.61) <0.001 ☨ Surgery 0.30 (0.26-0.36) <0.001 0.34 (0.29-0.40) <0.001 ☨ Chemo 0.26 (0.22-0.32) <0.001 0.22 (0.18-0.27) <0.001 ☨ Radiation 0.62 (0.55-0.70) <0.001 0.79 (0.70-0.90) <0.001 ☨ Survival analysis adjusted for race, sex, onset, area of living, MSI status and stage. Income was not included due to a VIF >10, suggesting collinearity. ☨: p value <0.05, statistically significant.