18f-fluorodeoxyglucose-positron emission tomography (FDG-PET) as a predictive biomarker in metastatic colorectal cancer (mCRC).

Abstract

e14120 Background:Information on the prognostic and predictive role of FDG-PET in the management of patients (pts) with mCRC is limited. The growing complexity of current therapies and the increasing number of agents to be tested in this disease warrants better understanding of the role of FDG-PET in earlier treatment decisions. Methods: Consecutive pts with 2 or more serial FDG-PET scans at baseline and during the treatment course were studied. Tumor standardized uptake value (SUV) and its percentage change (%DSUV) were each studied for their potential association with time to progression (TTP) via univariate Cox models to estimate the hazard ratio (HR) for progression. Results: 31 pts (median age 58.4 yrs) with mCRC were studied. 87% of pts were treated in the first line setting. 48% had received prior adjuvant therapy. 61%, 22% and 13% received oxaliplatin based, irinotecan based, and fluropyrimidine only regimens, respectively. 84% received concurrent bevacizumab. Median pretreatment SUV was 9.0 (range 1.7-46.0); median post treatment SUV was 4.0 (range 0 - 13.5); median %DSUV was -70.7 (range -10% to -100%). Median interval between scans was 3.0 months. 9 (29%) patients had no tumor uptake on post treatment scans. 55% and 39% of pts had partial response and stable disease (RECIST criteria), respectively. Median TTP was 11.9 months (90% CI: 9.9–13.7 mos), with a median follow-up time for progression of 15.4 months. The HRs for baseline SUV and %DSUV were 1.009 (90% CI: 0.978–1.040, p = 0.635) and 1.014 (90% CI: 1.002–1.026, p = 0.049), respectively. Among the 20 pts with inter-scan interval < 4 months, the median TTP of pts with posttreatment SUV = 0 was 9.7 months vs. 6.6 months for pts with post-treatment SUV > 0. TTP duration did not differ significantly (p = 0.085). Conclusions: Systemic therapy substantially decreased the SUV on follow up PET scans in pts treated for mCRC. However, no significant association was seen between either baseline SUV or %DSUV and TTP. Further work is needed to optimize and standardize evaluation of tumor response in mCRC patients with FDG- PET. No significant financial relationships to disclose.