Abstract
BackgroundPreoperative radiochemotherapy (RCT) is standard in locally advanced rectal cancer (LARC). Initial data suggest that the tumor’s metabolic response, i.e. reduction of its 18 F-FDG uptake compared with the baseline, observed after two weeks of RCT, may correlate with histopathological response. This prospective study evaluated the ability of a very early metabolic response, seen after only one week of RCT, to predict the histopathological response to treatment.MethodsTwenty patients with LARC who received standard RCT regimen followed by radical surgery participated in this study. Maximum standardized uptake value (SUV-MAX), measured by PET-CT imaging at baseline and on day 8 of RCT, and the changes in FDG uptake (ΔSUV-MAX), were compared with the histopathological response at surgery. Response was classified by tumor regression grade (TRG) and by achievement of pathological complete response (pCR).ResultsAbsolute SUV-MAX values at both time points did not correlate with histopathological response. However, patients with pCR had a larger drop in SUV-MAX after one week of RCT (median: -35.31% vs −18.42%, p = 0.046). In contrast, TRG did not correlate with ΔSUV-MAX. The changes in FGD-uptake predicted accurately the achievement of pCR: only patients with a decrease of more than 32% in SUV-MAX had pCR while none of those whose tumors did not show any decrease in SUV-MAX had pCR.ConclusionsA decrease in ΔSUV-MAX after only one week of RCT for LARC may be able to predict the achievement of pCR in the post-RCT surgical specimen. Validation in a larger independent cohort is planned.
Highlights
Preoperative radiochemotherapy (RCT) is standard in locally advanced rectal cancer (LARC)
Few studies reported an earlier prediction of histopathological response in LARC based on positron emission tomography (PET)-computerized tomography (CT) performed during RCT [13,14,15,16,17,18,19]
Data on prediction of response to preoperative therapy for LARC using early metabolic response as a surrogate are still very limited, and are almost invariably based on PET-CT done toward the midst of RCT
Summary
Preoperative radiochemotherapy (RCT) is standard in locally advanced rectal cancer (LARC). Initial data suggest that the tumor’s metabolic response, i.e. reduction of its 18 F-FDG uptake compared with the baseline, observed after two weeks of RCT, may correlate with histopathological response. This prospective study evaluated the ability of a very early metabolic response, seen after only one week of RCT, to predict the histopathological response to treatment. Preoperative radiochemotherapy (RCT) is standard in locally advanced rectal cancer (LARC) [1,2,3] This treatment is highly effective; tumor down-staging is common and in 15-30% of patients a pathological complete response (pCR) is achieved [4,5]. The purpose of our study was to prospectively evaluate the ability of a very early metabolic response, after only one week of RCT, to predict response to treatment
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