Tumor Volume Reduction Rate Predicts Pathologic Tumor Response of Locally Advanced Rectal Cancer Treated with Neoadjuvant Chemotherapy alone: Results from a Prospective Trial

Purpose: To evaluate tumor volume reduction rate (TVRR) measured by three-dimensional region-of-interest (3D-ROI) magnetic resonance (MR) volumetry in predicting pathological tumor response of preoperative chemotherapy alone for locally advanced rectal cancer (LARC). Methods: LARC patients who received neoadjuvant chemotherapy only from a prospective and randomized trial were recruited. Tumor volumes were measured with 3D-ROI MR volumetry. TVRR was determined using the equation TVRR = (V(Pre-Therapy) - V(Post-Therapy)) / V(Pre-Therapy) ×100%. Correlation between TVRR and clinical or pathological characteristics and predictive value of TVRR for pathological tumor response in terms of Tumor Regression Grade (TRG), T downstage, N downstage and overall downstage were analyzed. Results: 80 eligible cases of LARC were included in our study with TVRR of (51.7±25.1) %. TVRR was higher in well-differentiated tumors compared with poor-differentiated tumors (P=0.040). TVRR was found to be related with TRG (P<0.001), T downstage (P<0.001) and overall downstage (P<0.001). Risk of achieving TRG 2/3 decreased to 57.5% (P=0.002) and odds of achieving overall downstage increase to 179.3% (P<0.001) when TVRR increased by every 10%. A sensitivity of 0.704 and specificity of 0.804 were calculated when ROC curve was constructed to predict TRG using TVRR with a cutoff of 65%. Conclusion: TVRR is correlated with TRG and overall downstage significantly in LARC patients treated with preoperative chemotherapy alone and shows great value in predicting favorable TRG and overall downstage with good sensitivity and specificity. It could be considered as a promising parameter candidate for efficacy evaluation.