Objective  To evaluate the effects of neoadjuvant chemoradiotherapy on anal function after intersphincteric resection (ISR) with low rectal cancer.

  Methods  A total of 103 patients were classified into the chemoradiotherapy (CRT) group and control group according to whether they received neoadjuvant chemoradiotherapy. Anal function was assessed using vectorial manometry, Saito function questionnaires, and Wexner incontinence scores.

  Results  The resting vector volume and squeezing vector volume of the CRT group were significantly lower than those of the control group prior to the operation. Both groups showed decreasing manometric results after ISR. However, all indices of the CRT group were significantly lower than those of the control group (P < 0.05). At 6 and 12 months after operation, the Saito questionnaire results reveal poor function for the CRT group compared with the control group, except for dyschesia. After 24 months, the stool frequency, ability to distinguish between feces and flatus, fragmentation, and alimentary restriction remained poor for the CRT group (P < 0.05). Although both groups showed decreasing Wexner scores with time, the score of the CRT group remained significantly higher than that of the control up to 24 months after operation.

  Conclusion  Neoadjuvant chemoradiotherapy significantly affects the anal sphincter function for intersphincteric resection with low rectal cancer. This effect continues for at least 2 years after operation.