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Predicting Histopathologic Response to Neoadjuvant Therapy

March 11, 2008
Written by: , Filed in: Nuclear Medicine
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Background
The present method of assessing pathologic response of soft-tissue sarcomas to treatment by CT size criteria (RECIST method) is unreliable.

The objective of a recent study was to prospectively compare the RECIST criteria with change in uptake of FDG as a predictor of tumor histopathologic tumor response.

The study has concluded that change in fluorodeoxyglucose (FDG) uptake represents an accurate method of predicting response of tumor to neoadjuvant therapy, and is superior to use of size criteria for this purpose.

Design
Prospective imaging trial.

Participants
42 adult patients with resectable biopsy-proven, high-grade soft-tissue sarcomas who underwent FDG PET-CT scan before and after neoadjuvant therapy consisting of chemotherapy with or without radiation therapy. Four patients with liposarcomas were excluded because baseline FDG uptake was <2.5. Methodology
Patients underwent FDG PET-CT before (1 to 14 days) and after (5 to 15 days) neoadjuvant therapy. Patients were operated on 1 to 18 days thereafter. Readers were blinded to extraneous information. Average standardized FDG uptake in a 1.5-cm diameter region was calculated for scans before and after therapy.

Tumor size was determined using the RECIST method before and after therapy. Resected tumor was graded for percentage necrosis, with 95% considered a histopathologic responder. Receiver operator characteristic (ROC) curves were generated for change in standardized uptake value (SUV) and RECIST values as predictors of histopathologic response.

CME Courses Available:

 

PET/CT and SPECT/CT To Plan and Monitor the Treatment of Cancer The precise tailoring of treatment for patients with cancer is an unmet challenge. The goal is to only administer treatments that have a high probability of being effective. Imaging with PET/CT and SPECT/CT provides methods that will help achieve this goal. The program covers the current clinical challenges, the new emerging answers from imaging, and how these methods can be applied to patient care. Read more: Nuclear Medicine: PET/CT and SPECT/CT

 

-- Diagnostic Imaging Review: For Residents, Fellows and Radiologists UCSF’s Department of Radiology and Biomedical Imaging recently conducted its annual radiology review course. It will soon be available in two video formats to meet your needs— DVD and MP4. Order now to get your special pre-publication discount. Read more or order: Diagnostic Imaging Review

Results of the Study
Tumor size (mean +/- SD) was 9.2 +/- 4.2 cm before, and 9.2 +/- 4.8 cm after therapy (not significant). SUV uptake was 9.2 +/- 6.7 before, and 4.6 +/- 3.4 after therapy (P <0.001). Mean percentage necrosis was 55% +/- 31%. Eight patients were histopathologic responders. Changes in tumor size did not correlate with histopathologic response (P =0.24). A change in RECIST was not sensitive for response (25%), although it was specific, and the area under the ROC curve was only 0.60. With response to FDG uptake, the area under the ROC curve was 0.93, which was statistically superior to RECIST criteria (P =0.004). Using a 60% reduction in FDG uptake as a cutoff, the sensitivity was 100% and the specificity was 71% for predicting response. Using a stricter cutoff of 70%, the sensitivity decreased to 75%, but specificity was 100%. Conclusions
Measuring change in tumor glucose uptake is superior to change in size as a predictor of tumor necrosis.

Reviewer’s Comments
This is the first study to compare size and FDG uptake criteria in the same patients. Use of ROC Methodology also is the appropriate method to compare modalities with modifiable thresholds of positivity, as in the case of size and FDG uptake criteria.

That said, it is surprising that the authors chose only to grade histopathology as a dichotomous variable, with response defined as 95% necrosis. Tumor necrosis could have been treated as a continuous variable and a correlation established between percentage necrosis and either changes in size or changes in FDG uptake. This is a very persuasive argument to perform FDG scanning for monitoring of these patients on therapy.

Author: Lionel S. Zuckier, MD

Reference
Evilevitch V, Weber WA, et al. Reduction of Glucose Metabolic Activity Is More Accurate Than Change in Size at Predicting Histopathologic Response to Neoadjuvant Therapy in High-Grade Soft-Tissue Sarcomas. Clin Cancer Res; 2008; 14 (February 1): 715-720.

CME Courses Available:

 

PET/CT and SPECT/CT To Plan and Monitor the Treatment of Cancer The precise tailoring of treatment for patients with cancer is an unmet challenge. The goal is to only administer treatments that have a high probability of being effective. Imaging with PET/CT and SPECT/CT provides methods that will help achieve this goal. The program covers the current clinical challenges, the new emerging answers from imaging, and how these methods can be applied to patient care. Read more: Nuclear Medicine: PET/CT and SPECT/CT

 

-- Diagnostic Imaging Review: For Residents, Fellows and Radiologists UCSF’s Department of Radiology and Biomedical Imaging recently conducted its annual radiology review course. It will soon be available in two video formats to meet your needs— DVD and MP4. Order now to get your special pre-publication discount. Read more or order: Diagnostic Imaging Review
.

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