Worse treatment response to neoadjuvant chemoradiotherapy in young patients with locally advanced rectal cancer.

<bold>Background: </bold>To evaluate the impact of age on the efficacy of neoadjuvant chemoradiotherapy (NCRT) in patients with locally advanced rectal cancer (LARC).<bold>Method: </bold>LARC patients undergoing NCRT and radical surgery from 2011 to 2018 were divided into young (< 40 years) and old (≥40 years) groups. Multivariate analyses were performed to identify predictive factors for pathological complete response (pCR). Predictive nomograms and decision curve analysis were used to compare the models including/excluding age groups. Immunohistochemical analysis was performed to detect CD133 expression in LARC patients.<bold>Result: </bold>A total of 901 LARC patients were analyzed. The young group was associated with poorly differentiated tumors, more metastatic lymph nodes, higher perineural invasion, and a lower tumor regression grade (P = 0.008; P < 0.001; P < 0.001; P = 0.003). Logistic regression analysis demonstrated that age < 40 years (HR = 2.190, P = 0.044), tumor size (HR = 0.538, P < 0.001), pre-NCRT cN stage (HR = 0.570, P = 0.036), and post-NCRT CEA level (HR = 0.877, P = 0.001) were significantly associated with pCR. Predictive nomograms and decision curve analysis demonstrated that the predictive ability of models including the age group was superior to that of models excluding the age group. Higher CD133 expression was more common in young LARC patients.<bold>Conclusion: </bold>Young patients with LARC were associated with lower pCR rates following NCRT. The ability of the predictive model was greater when based on the age group. Young LARC patients were associated with a higher CD133+ tumor stem cell burden, which contributed to the lower pCR rates. [ABSTRACT FROM AUTHOR]