To investigate the value of endorectal ultrasonography (ERUS) in preoperative assessment of rectal cancer post neoadjuvant chemoradiation therapy.

From Jan. 2016 to Dec. 2016, 90 rectal cancer patients who underwent preoperative neoadjuvant chemoradiation therapy and total mesorectal excision surgery in the Sixth Affiliated Hospital of Sun Yat-Sen University were retrospectively analyzed, and all patients underwent ERUS examination post neoadjuvant chemoradiation therapy. Of these, 64 patients were evaluated by ERUS pre and post neoadjuvant chemoradiation therapy and 26 patients were evaluated only post neoadjuvant chemoradiation therapy. Wilcoxon rank sum test for paired sample was performed to compare the distance from inferior margin of tumor to anal margin, the length and thickness of the tumor pre and post neoadjuvant chemoradiation therapy respectively in rectal cancer. Taken pathologic findings as golden standard, the accuracy of T staging assessed by ERUS post neoadjuvant chemoradiation therapy was evaluated.

Compared with pre neoadjuvant chemoradiation therapy, the distance from inferior margin of tumor to anal margin significantly increased after neoadjuvant chemoradiation therapy [(58.63±21.71) mm vs (51.68±19.81) mm], and the length [(26.10±10.07) mm vs (40.82±9.18) mm] and thickness [(9.73±2.50) mm vs (14.92±5.30) mm] of tumor also evidently decreased post neoadjuvant chemoradiation therapy, respectively (Z were 4.996, 6.153 and 6.076, all P<0.01). The final pathological T stage was pathologic complete response (pCR) or pT0 in 15 patients, pT1 in 3 patients, pT2 in 30 patients and pT3 in 42 patients. The diagnostic accuracy of T staging of rectal cancer post neoadjuvant chemoradiation therapy for ERUS was uT0 82.2% (74/90), uT1 96.7% (87/90), uT2 66.7% (60/90), uT3 67.8% (61/90) and uT4 96.7% (87/90), and the overall accuracy was 82.2% (74/90).

ERUS could effectively record the morphological changes of rectal cancer pre and post neoadjuvant chemoradiation therapy, which may contribute to the re-evaluation of the distance from inferior tumor margin to anal margin and the range and depth of tumor involvement pre surgical resection.