18F-FDG PET is an early predictor of pathologic tumor response to preoperative radiochemotherapy in locally advanced rectal cancer

F-18-FDG PET is a useful tool for assessing the effects of chemo- or radiotherapy. The aim of this study was to correlate the change in tumor F-18-FDG standardized uptake value (SUV) during and after preoperative radiochemotherapy, with the pathologic response achieved in locally advanced rectal cancer (LARC) patients. Methods: Thirty-three patients with LARC underwent total mesorectal excision after preoperative treatment, including 3 cycles of oxaliplatin, raltitrexed, 5-fluorouracil, and folinic acid during pelvic radiotherapy (45 Gy). Staging procedures included endoscopic ultrasound, MRI, and CT. F-18-FDG PET scans were performed at baseline and 12 d after starting radiochemotherapy (intermediate) in all patients. Seventeen patients also had a presurgical scan. For each scan, mean and maximum SUVs were measured. The percentages of SUV decrease from baseline to intermediate (early change) and to presurgical scan (overall change) were assessed and correlated with pathologic response classified as tumor regression grade (TRG). Results: Eighteen tumors (55%) showed complete (TRG1) or subtotal regression (TRG2) and were classified as responders, whereas 15 cases (45%; TRG3 or TRG4) were considered nonresponders. The early median decrease of tumor SUV significantly differed between responders (-62%; range, -44% to -100%) and nonresponders (-22%; range, -2% to -48%). A significant correlation was also found between TRGs and early SUV changes (P < 0.0001). Responders were identified correctly by an early decrease of the mean SUV of >= 52%. Conclusion: This study shows that early F-18-FDG PET can predict pathologic response to preoperative treatment. These findings support the usefulness of F-18-FDG PET during the management with radiochernotherapy of LARC patients.