Semi-Quantitative Calculations of Primary Tumor Metabolic Activity Using F-18 FDG PET/CT as a Predictor of Survival in 92 Patients With High-Grade Bone or Soft Tissue Sarcoma

10583 Background: Surrogate endpoints for survival are needed to allow rapid assessment of new therapies without doing lengthy studies using a survival endpoint. Non-invasive assessment of treatment response is also needed to guide chemotherapy. FDG- PET-CT has potential for assessing response to treatment in sarcoma. This study's goal was to correlate FDG-PET-CT, along with standard CT, with histologic response after chemotherapy for high grade soft tissue sarcomas before resection. Methods: Patients with high grade soft tissue sarcomas > 5 cm were enrolled in a prospective clinical trial and given ifosfamide/doxorubicin before tumor excision. FDG-PET-CT was performed at baseline before treatment, after cycle 1, & just before surgery. Differences in both SUVmax (baseline to cycle 1 [B-1], baseline to surgery [B-3]) and CT criteria (RECIST 1 dimension [1D], RECIST 2D & Choi) were compared to histologic response (> or < 90%) upon excision. Results: 25 patients were enrolled and 4 had disease progression prior to completing all 3 PET-CT's yielding 21 evaluable cases. 5 patients had SUVmax change of <40%: 4/5 (80%) had histologic response < 90% & 1/5 (20%) had histologic response >90%. 16 patients had SUVmax change of >40%: 12/16 (75%) had histologic response >90% & 4/16 (25%) had histologic response <90%. A scatterplot of SUVmax change (baseline to surgery), & histologic response as continuous variables revealed a Spearman's correlation coefficient = 0.55 (p<0.01). Conclusions: A cutoff value of 40% reduction in SUVmax from baseline to surgery appeared to differentiate histologic responders. Using this to define PET response, a correlation between PET response, as well as RECIST 1D and 2D, and histologic response was observed. Additional patient follow-up & further study of FDG-PET-CT as a surrogate endpoint for histologic response and survival is warranted. [Table: see text] [Table: see text]

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Change in quantitative FDG-PET was significantly more accurate than change in size at predicting histopathologic response to neoadjuvant therapy in high grade soft tissue sarcomas

Journal of Clinical Oncology ◽

10.1200/jco.2007.25.18_suppl.10017 ◽

2007 ◽

Vol 25 (18_suppl) ◽

pp. 10017-10017

Author(s):

V. Evilevitch ◽

W. A. Weber ◽

W. D. Tap ◽

K. Chow ◽

M. Allen-Auerbach ◽

...

Keyword(s):

Soft Tissue ◽

Neoadjuvant Therapy ◽

Tumor Size ◽

Fdg Pet ◽

Soft Tissue Sarcomas ◽

High Grade ◽

Fdg Uptake ◽

Histopathologic Response ◽

Pet Ct ◽

Fdg Pet Ct

10017 Background: Change in size by RECIST (Response Evaluation Criteria in Solid Tumors) has been the standard to assess response to therapy in non-GIST soft tissue sarcomas (STS). Although recent studies have demonstrated that Positron Emission Tomography with F18-fluorodeoxyglucose (FDG-PET) may be used to assess response, there has not been a direct comparison between these modalities. The aim of this study was to prospectively evaluate whether a change in quantitative FDG-PET or a change in size [computed tomography(CT)] was more accurate at predicting histopathologic response to neoadjuvant therapy in patients with high grade STS using a combined FDG-PET/CT scan. Methods: From 1/05 - 12/06 58 patients with resectable biopsy proven high grade STS scheduled to undergo neoadjuvant chemotherapy were prospectively enrolled in this study. Patients underwent FDG-PET/CT prior to and after neoadjuvant treatment (prior to surgery). Tumor FDG-uptake was quantified by standardized uptake values (SUV). Changes in tumor size were quantified according to RECIST. Following tumor resection, response was assessed histopathologically. Patients with = 10% viable tumor cells were classified as responders. To date, 36 patients have completed the study and are the subject of this analysis. Results: In histopathologic responders (n=10, 28%), reduction of tumor FDG-uptake was significantly greater (-64%) than in histopathologic non-responders (-37%), (p=0.005). Using a 50% decrease in tumor SUV as a threshold value resulted in a sensitivity of 90% and a specificity of 58% for assessment of histopathologic response (p=0.01). Response assessment per RECIST showed no significant correlation with histopathologic response (sensitivity 20%, specificity 89%, p=0.4). There was no correlation between changes in tumor size and histopathologic response (area under the ROC curve = 0.6, p=0.1). Conclusions: In patients with high grade STS, quantitative FDG-PET was significantly more accurate than size based criteria for assessment of histopathologic response to neoadjuvant therapy. FDG-PET should be considered as a modality to monitor treatment response is patients with high grade STS. No significant financial relationships to disclose.

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