ABSTRACT
To assess the value of endorectal ultrasonography ( ERUS ) in predicting the pathological response to neoadjuvant chemoradiotherapy( NCRT ) for locally advanced rectal cancer( LARC) . Methods Ninety‐nine patients with LARC received NCRT and total mesorectal excision in our hospital were retrospectively analyzed . T he maximum length and thickness of rectal tumor were measured by ERUS both before NCRT ( ERUS1 ) and after NCRT following sugery ( ERUS2 ) ,and the length and thickness reduction rate were calculated . T he patients were classified into good responder group ( n ＝ 47 ) and poor responder group( n ＝ 52 ) ,or pathological complete response ( pCR) group ( n ＝ 25 ) and non‐pCR group ( n＝74) according to pathological tumor regression grade ( T RG ) . T he differences of various parameters were compared between groups . T he correlations between these parameters and T RG grading were analyzed by Spearman correlation analysis . T he ROC curve was used to evaluate the diagnostic efficacy of the parameter . Results T he length and thickness of ERUS2 were significantly shorter than that of ERUS1( all P ＜0 .05) . T he length and thickness of ERUS2 in good responder group were shorter than those in poor responder group ,while the length and thickness reduction rate were higher than those in poor responder group with significant difference ( all P ＜ 0 .05 ) . T he length and thickness of ERUS2 in pCR group were shorter than those in non‐pCR group ,w hile the length and thickness reduction rate were higher than those in non‐pCR group with significant difference ( all P ＜ 0 .05 ) . T he length and thickness of ERUS2 were positively correlated with T RG grading ( r ＝ 0 .577 ,0 .605 ; all P ＜ 0 .01 ) and the length and thickness reduction rate were negatively correlated with T RG grading ( r ＝ －0 .681 ,－0 .598 ; all P ＜0 .01 ) . ROC curve showed the cut‐off value of the length and thickness reduction rate to predict good responder were 41 .34% ,46 .46% , with corresponding AUC areas of 0 .843 ,0 .796 , sensitivity of 74 .5% ,70 .2% , and specificity of 76 .9% ,80 .8% ,respectively . ROC curve showed the cut‐off value of the length and thickness reduction rate to predict pCR were 57 .36% ,58 .52% ,with corresponding AUC areas of 0 .851 and 0 .895 , sensitivity of 68 .0% ,76 .0% ,and specificity of 94 .6% ,93 .2% ,respectively . Conclusions T he changes of length and thickness of tumor after NCRT are well correlated with treatment response . T he length and thickness reduction rate measured on ERUS present high accuracy in prediction of good response and pCR in LARC patients .