428P Association between three dimensional transrectal ultrasound findings and tumor response in locally advanced rectal cancer

Abstract

For locally advanced rectal cancer (LARC) patients, neoadjuvant chemoradiotherapy (NACRT) followed by total mesorectal excision (TME) is the standard treatment. However, the accuracy of evaluating complete response with non-pathological method is limited and a more powerful method is needed. The aim of this study was to assess the capability of Three Dimensional Transrectal Ultrasound (3D-TRUS) in predicting the response of rectal cancer to neoadjuvant chemoradiotherapy (NACRT). Patients with locally advanced rectal cancer and with ycT0-T3a after NACRT were enrolled. 3D-TRUS was performed at 7 weeks after the end of CRT. The association between pathological tumor response (TRG = 0 or TRG > 0) and 3D-TRUS parameters were analyzed. These parameters included thickness of muscularis, thickness of contralateral muscularis, leison angle range, regularity of the shape, integrity of mucous layer, bluration of margin, internal echo, and posterior echo. A total of 101 patients were recruited, including 72 cases recieved TME, and 29 cases underwent Watch & Wait. In the dataset with 72 cases recieved TME, adjusted-thickness of muscularis (P < 0.001), leision angle range (P < 0.001), leision normalized-size (P < 0.001) and regularity of the leision shape (P < 0.001) were strongly associated with tumor response. Three parameters were kept in the logistic model: leision normalized-size (OR = 4.98, 95% CI = 1.63-15.17, P = 0.005), regularity of the leision shape (OR = 20.03, 95% CI = 1.84-217.89, P = 0.014), and bluration of leision margin (OR = 17.01, 95% CI = 1.51-191.25, P = 0.022), and the AUC of the logistic model was 0.89. Among these parameters, leision normalized-size was the most powerful variable. Additionally, we got similar results in the whole population of 101 case and in the cross validation. The 3D-TRUS based model has a good discrimination for predicting tumor response in rectal cancer patients with NACRT, and it should be included as a part of criterion for evaluating cCR.