FDG-PET/CT (PET) in the early prediction of benefit from first-line chemotherapy plus bevacizumab (bev) in metastatic colorectal cancer (mCRC).

Abstract

e14531 Background: The conventional assessment of response according to RECIST seems not optimal to estimate the actual benefit from antiangiogenic agents. A recent experience suggests the potential role of PET in the early prediction of benefit from first-line chemotherapy in mCRC. The objective of the present study was to evaluate the metabolic PET response to one single cycle of chemotherapy plus bev in mCRC patients (pts). Methods: PET was carried out at baseline and on day 13 in 51 unresectable mCRC pts, treated with biweekly bev-containing regimens; computed tomography (CT) scan was performed at baseline and every 2 months. PET response was defined by >15% decrease in FDG uptake in the dominant proportion of lesions, in the absence of metabolically progressive lesions. CT response was defined according to RECIST 1.0. Results: PET response rate was 73%. PET responders achieved longer PFS compared to PET non-responders (median PFS: 11.0 vs 8.3 months; HR=0.45 [95%CI 0.14-0.93] p=0.035). RECIST CT response rate was 62% and 57%, in PET responders and non-responders, respectively (p=0.76). At an exploratory analysis, among pts (N=15) reporting a RECIST-defined stable disease (SD), those with a percentage decrease in FDG uptake higher than the median value (>33%) had significantly longer PFS in comparison to those with a lower PET response (median PFS: 9.4 vs 7.4 months; HR=0.2 [95%CI 0.005-0.24] p=0.0006). Conclusions: Early PET response, assessed after one single cycle of chemotherapy plus bev, predicts PFS, while it does not correlate with traditional RECIST response. In the subgroup of pts reporting a RECIST SD, the early reduction in FDG uptake correlates with PFS. On the basis of our results, early PET response on day 13th could representan early predictor of benefit from bev plus chemotherapy in mCRC.