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Neither FDG-PET Nor CT Can Distinguish Between a Pathological Complete Response and an Incomplete Response After Neoadjuvant Chemoradiation in Locally Advanced Rectal Cancer: A Prospective Study

Guillem, José G. MD*; Ruby, Jeannine A. MD*; Leibold, Tobias MD*; Akhurst, Timothy J. MD; Yeung, Henry W. MD; Gollub, Marc J. MD; Ginsberg, Michelle S. MD; Shia, Jinru MD; Suriawinata, Arief A. MD; Riedel, Elyn R. MA§; Mazumdar, Madhu PhD§; Saltz, Leonard B. MD; Minsky, Bruce D. MD; Nash, Garrett M. MD*; Paty, Philip B. MD*; Temple, Larissa K. MD*; Weiser, Martin R. MD*; Larson, Steven M. MD

doi: 10.1097/SLA.0b013e318277b625
Original Articles
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Objective: To prospectively compare the ability of flourodeoxyglucose-positron emission tomography (FDG-PET) and computed tomography (CT) to identify a pathological complete response (pCR) in patients with rectal cancer treated by chemoradiation.

Background: A major obstacle in pursuing nonoperative management in patients with rectal cancer after chemoradiation is the inability to identify a pCR preoperatively.

Methods: A total of 121 patients with rectal cancer were prospectively enrolled. FDG-PET scans and helical CT scans were obtained before and after neoadjuvant chemoradiation. Consensus readings of PET and CT scans were used to classify certainty of disease (5-point confidence rating scale). The ability of PET and CT scans to accurately distinguish a pCR (ypT0) from an incomplete response (ypT1–4) was estimated using the area under the receiver operating characteristic curve (AUC).

Results: Of the 121 patients, 26 (21%) had a pCR. PET and CT scans were equally inadequate at distinguishing a pCR from an incomplete response (AUC = 0.64 for both, P = 0.97). Among the 26 patients with a pCR, 14 (54%) and 5 (19%) were classified as complete responders on PET and CT scans, respectively. Among the 95 patients with an incomplete pathological response, 63 (66%) and 90 (95%) were classified as incomplete responders on PET and CT scans, respectively. None of the individual PET parameters, including visual response score, mean standard uptake value (SUVmean), maximum SUV (SUVmax), and total lesion glycolysis, accurately distinguished a pCR (AUCs = 0.57–0.73).

Conclusions: Neither PET nor CT scans have adequate predictive value to be clinically useful in distinguishing a pCR from an incomplete response and, therefore, should not be obtained for the purpose of attempting to predict a pCR after neoadjuvant chemoradiation for rectal cancer.

One hundred twenty-one patients with rectal cancer underwent FDG-PET and computed tomography before and after neoadjuvant chemoradiation. Neither FDG-PET (confidence rating of disease, standard uptake value, total lesion glycolysis, tumor volume, visual response score) nor computed tomography (confidence rating of disease, visual response score) accurately distinguished a pathological complete response from an incomplete response.

Departments of *Surgery

Radiology

Pathology

§Epidemiology and Biostatistics

Medicine, and

Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY.

Dr Tobias Leibold is now with the Department of General and Visceral Surgery, Robert-Bosch Hospital, Stuttgart, Germany; Dr Timothy J. Akhurst is now with the Department of Nuclear Medicine, Peter MacCallum Cancer Centre, East Melbourne, Australia; Dr Henry W. Yeung is now with the Department of Nuclear Medicine, Hong Kong Sanatorium & Hospital, Hong Kong, China; Dr Arief A. Suriawinata is now with the Department of Pathology, Dartmouth-Hitchcock Norris Cotton Cancer Center, Lebanon, NH; Dr Madhu Mazumdar is now with the Department of Public Health, Division of Biostatistics and Epidemiology, Weill Cornell Medical College, New York, NY; and Dr Bruce D. Minsky is now with the Department of Radiation and Cellular Oncology, University of Chicago Medical Center, Chicago, IL.

Reprints: José G. Guillem, MD, Department of Surgery, Memorial Sloan-Kettering Cancer Center, 1275 York Ave, Room C-1077, New York, NY 10065. E-mail guillemj@mskcc.org.

This work was presented at the American College of Surgeons 97th Annual Clinical Congress, San Francisco, CA, October 23 to 27, 2011.

Disclosure: This study was supported in part by National Cancer Institute grant no. RO1 CA 82534 (to J.G.G.) ClinicalTrials.gov Identifier: NCT00004891. The authors declare no conflicts of interest.

© 2013 by Lippincott Williams & Wilkins.