Clinical influence of cancer stem cells on residual disease after preoperative chemoradiotherapy for rectal cancer

We evaluated the clinical influence of cancer stem cells (CSCs) on residual disease after preoperative chemoradiotherapy (CRT) in patients with rectal cancer. The surgical specimens of 145 patients with residual rectal cancer after preoperative CRT were assessed. To identify CSCs, immunohistochemistry was performed using their surrogate makers (CD44 and aldehyde dehydrogenase 1 [ALDH1]) in full section tissues. Of the 145 cases, ALDH1 and CD44 positivity was found in 80.0 % (n = 116) and 47.6 % (n = 69), respectively; ALDH1 positivity showed weakly positive correlation with CD44 (r _s  = 0.269, P = 0.002). ALDH1 and CD44 positivity was related to lower tumor regression grade (TRG) (P = 0.009 and 0.003, respectively). Additionally, ALDH1 positivity was associated with positive circumferential resection margin (P = 0.019). However, ALDH1 and CD44 positivity showed no relationship with KRAS or BRAF mutation. In univariate analysis, ALDH1 positivity was associated with short recurrence-free survival (RFS) (P = 0.005) and rectal cancer-specific survival (RCSS) (P = 0.043), but not CD44 positivity (RFS, P = 0.725; RCSS, P = 0.280). In multivariate analysis, ALDH1 positivity was an independent prognostic factor for poor RFS (P = 0.039; hazard ratio = 2.997; 95 % confidence interval = 1.059–8.478), but not RCSS (P = 0.571). The expression of ALDH1 assessment independently predicts RFS in patients with residual disease after CRT. These results suggest that targeting CSCs could be an effective therapeutic approach to rectal cancer patients receiving preoperative CRT.