Early reduction of FDG uptake predicts pathologic tumor response to preoperative radio-chemotherapy in locally advanced rectal cancer

Abstract

131

Objectives: Monitoring of FDG uptake is useful for assessing the effects of chemo and/or radiotherapy. Aim of this study is to correlate the standardized uptake value (SUV) changes during and after preoperative radio-chemotherapy, with pathologic response in locally advanced rectal cancer (LARC) patients.

Methods: We are evaluating patients with LARC undergoing neoadjuvant radio-chemotherapy (three cycles of oxaliplatin, raltitrexed, 5-fluorouracil and folinic acid during pelvic radiotherapy with 45 Gy) prior to total mesorectal excision. Patients are staged using endoscopic ultrasound, magnetic resonance imaging and computed tomography. FDG-PET is performed at baseline for staging purposes and repeated 12 days after the beginning of radio-chemotherapy (intermediate scan) and prior to surgery. SUV changes within the primary tumor are monitored by ROI analysis of the studies. Percentage of SUV decrease from baseline to intermediate (early change) and from baseline to presurgical scan (overall change) are being assessed and correlated with pathologic response classified as tumor regression grade (TRG). We have completed the analysis on thirty three patients.

Results: Eighteen tumors (55%) showed complete (TRG1) or subtotal (TRG2) pathological regression and were classified as responders, whereas 15 cases (45%, showing TRG3 or TRG4) were considered non-responders. The early median decrease of tumor SUV significantly differed between responders (-62%) and non-responders (-22%). A significant correlation was also found between TRGs and early SUV changes (p<.0001). Responders were correctly identified by an early decrease of SUV-mean ≥ 52%.

Conclusions: This study shows that FDG-PET performed early during the course of neoadjuvant radio-chemotherapy can predict pathologic response to treatment. These findings support the use of FDG-PET during LARC as a prognostic tool to aid in surgical and medical treatment decision making.