Use and benefit of adjuvant chemotherapy in early- vs average-onset colorectal cancer.

Abstract

3615 Background: Despite improved mortality rates in colorectal cancer (CRC), the incidence of early onset-colorectal cancer (EO-CRC) has been rising in the United States. We aimed to explore trends in adjuvant chemotherapy (ACT) administration and evaluate its impact on overall survival (OS) and cancer-specific survival (CSS) in patients with EO-CRC (< 50 years old) and average-onset colorectal cancer (AO-CRC) [> 50 years old]. Methods: Adult patients (age >18) with Stage II-low risk (T1-T3 disease and more than 12 lymph nodes examined), stage II-high risk (T4 disease or less than 12 total lymph nodes examined) or stage III CRC diagnosed between 2010-2020 were identified in the Surveillance, Epidemiology, and End Results Program (SEER) Database. Cox proportional hazard models were used to assess the effect of ACT on OS and CSS in patients with EO-CRC and AO-CRC. Results: The final dataset included 8,998 patients with EO-CRC and 64,987 patients with AO-CRC (Stage II-low =27,446, Stage II-high =9,060, and Stage III = 37,479). Patients with AO-CRC were less likely to receive ACT compared to patients with EO-CRC across all stages: stage II-low (odds ratio [OR]: 0.27), stage II-high (OR 0.28), and stage III (OR: 0.32). From 2010 to 2020, the use of ACT decreased for EO-CRC (68% to 64%) but increased for AO-CRC (36% to 45%). In patients with AO-CRC, ACT improved OS and CSS in stage II-high (OS Hazard ratio(HR]:0.48, 95%CI 0.42-0.54; CSS HR:0.48, 95%CI 0.42-0.54) and stage III (OS HR:0.38, 95%CI 0.37-0.40; CSS HR:0.38, 95%CI 0.37-0.40), but had no benefit in CSS for stage II-low disease (CSS HR: 1.01, 95%CI 0.84-1.22). In patients with EO-CRC, ACT improved OS (HR 0.70, 95% CI 0.56-0.88) and CSS (HR: 0.70, 95% CI 0.56-0.88) in stage III disease. No statistically significant survival benefit was observed for patients with stage II-low (CSS HR:1.11, 95%CI 0.66-1.86) or stage II-high (CSS HR:0.83, 95%CI 0.53-1.31).The 5-year survival probabilities by stage are shown in the table. Conclusions: Despite being used more frequently, the benefit of ACT in EO-CRC seems to be of less magnitude than in AO-CRC. These differences might be partially explained by the better survival outcomes of EO-CRC even without ACT. Though recommended by most clinical guidelines, ACT does not improve survival outcomes in patients with stage II high-risk EO-CRC. These findings highlight the need to improve risk stratification in early stage EO-CRC to better identify patients who may benefit from ACT. 5-Year survival probabilities by stage (II-Low, II-High, III). Variable OS II-Low OS II-High OS III CSS II-Low CSS II-High CSS III AO; Chemo 84.77% 72.51% 69.66% 88.86% 76.96% 75.08% AO; No Chemo 74.11% 53.47% 41.54% 89.63% 70.93% 56.55% EO; Chemo 93.53% 84.34% 78.72% 94.54% 86.34% 80.18% EO; No Chemo 93.68% 80.19% 71.77% 95.32% 84.28% 75.84%