Abstract 1135
Background
Neoadjuvant chemoradiotherapy (CRT) is standard in locally advanced rectal cancer (LARC). Current data on the predictive value of early PET/CT, i.e. the correlation between the tumor’s early metabolic response, manifested by the reduction of its 18F-FDG uptake after two weeks of CRT compared with baseline, and histopathological response, are conflicting.
Methods
Patients (pts) with histologically confirmed LARC who were planned to receive standard CRT regimen of 50.4 Gray radiotherapy with concurrent fluoropyrimidine–based chemotherapy followed by radical surgery were eligible for the study. Baseline PET/CT was done within 4 weeks prior to CRT and the investigational scan was done two weeks+/-two days after its initiation. Maximum standardized uptake value (SUV-MAX) and the changes in FDG uptake between the two scans (ΔSUV-MAX) were compared with the histopathological response at surgery. Response was classified by tumor regression grade (TRG) and presence of pathological complete response (pCR).
Results
Twenty pts were included in the study, 65% with clinical stage II and 35% with stage III. Ninety percents of tumors were located at least 5 cm from the anal verge. Pts underwent surgery within a median of 8.6 weeks (4.5-12.8) after the completion of CRT. Six pts (30%) achieved pCR and 7 (35%) had TRG I-II. Absolute SUV-MAX values at both time points did not correlate with pCR (p = 0.099) nor with TRG (p = 0.670). Histopathological response also did not correlate with ΔSUV-MAX: pts who achieved pCR had median ΔSUV-MAX of -45%, while those who did not had median ΔSUV-MAX of -41% (p = 0.617). Similarly, pts with TRG I-II and those with TRG III-IV had the same median ΔSUV-MAX of -42% (p = 0.882). In addition, using ROC analysis we did not find any cutoff of any the PET-CT parameters that will predict pCR or TRG I-II.
Conclusions
In the current study, early PET/CT done after two weeks of neoadjuvant CRT for LARC, failed to predict histopathological response to treatment.
Clinical trial identification
Legal entity responsible for the study
Rabin Medical Center.
Funding
Has not received any funding.
Editorial Acknowledgement
Disclosure
All authors have declared no conflicts of interest.
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