Histopathologic analysis of the anal sphincter after chemoradiation for low rectal cancer

Background/Purpose: Neoadjuvant chemoradiation is considered to be the treatment of choice for locally advanced rectal cancer. However, patient-oriented outcomes and postoperative quality of life are unsatisfactory. In this study, we analyze histopathologic changes in the sphincter apparatus in patients who received abdominoperineal resection with or without preoperative chemoradiation. Methods: Patients with low rectal cancer who underwent abdominoperineal resection from January 2009 to October 2009 were retrospectively enrolled and reviewed. The specimens obtained from the patients were stained using hematoxylin and eosin, Masson's trichrome and S-100 immunoperoxidase. Semi-quantitative assessment of the fibrous replacement and nerve bundle densities were analyzed. Results: Eleven patients were retrospectively chart reviewed [one female, 10 males; mean age 63 years (range, 48-77 years)]. Six patients with locally advanced disease staged by pelvic magnetic resonance imaging were treated with preoperative chemoradiation followed by surgical resection. The other five patients underwent surgery without chemoradiation (control group). There was a trend toward increased fibrosis in the patients receiving chemoradiation. Fibrous replacement was also detected in the area surrounding the tumor. In Meissner's plexus (submucosal plexus), there was no difference in nerve density between the two groups; however, in Auerbach's plexus (myenteric plexus), there was an increased density of nerve bundles in the chemoradiation group. Conclusion: Neoadjuvant chemoradiation causes histopathologic changes in the anorectal region by increasing fibrous replacement and altering nerve bundle arrangement. These alterations may interfere with bowel function including a decrease in anorectal resting pressure, soiling and an incomplete defecation sensation. Further studies with larger patient samples are necessary for clarification.