Correlation of FDG PET-CT with histologic response after neoadjuvant chemotherapy for soft tissue sarcomas

Abstract

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]