Early predictive value of 18F-FDG-PET assessment in advanced esophagogastric junction and gastric cancer patients treated with cetuximab-containing therapy

Abstract

e15601 Background: 18F-FDG-PET/CT (PET) was reported to predict the pathological response during preoperative chemotherapy in esophagogastric junction (GEJ) or gastric (G) cancer pts. The aim of this study is to evaluate the usefulness of an early change in PET at several time-points in predicting response to cetuximab-containing therapy in pts with advanced GEJ or G cancer. Methods: We evaluated 51 pts with locally advanced/metastatic GEJ or G adenocarcinoma who underwent a first line cetuximab- treatment in two Italian phase II studies. Twenty nine pts (GEJ/G = 5/24; locally advanced/metastatic = 2/27) received cetuximab in combination with cisplatin/docetaxel (DOCETUX study) and 22 pts (GEJ/G = 2/20; locally advanced/metastatic = 3/19) received cetuximab in combination with FOLFIRI (FOLCETUX Study). PET scans were performed at baseline, and in FDG-avid pts, again on day 21 in the DOCETUX study and on day 42 in the FOLCETUX study. Metabolic response was defined as a decrease in maximum standard uptake value (SUV) ≥35% on the basis of our previous study (Di Fabio et al., Gastric Cancer 10:221–227, 2007).Objective response, according to RECIST criteria, was assessed by CT scan at baseline and every 6 weeks. Results: Five pts (10.2%) had FDG non- avid tumor (all pts with signet cell carcinoma). In the 46 FDG-avid tumor pts, the median SUV at baseline was 10.3 (range 5.0 - 36.4). The response rate (RR) was significantly higher in pts with a drop ≥35% in SUV from baseline to day 42: 83% (10/12 pts) in metabolic responders vs. 25% (2/8 pts) in non-metabolic responders (p= 0.019). In contrast, the SUV change at day 21 did not correlate with objective response: RR 57.1% (8/14 pts) in metabolic responders vs. 41.7% (5/12 pts) in non-metabolic responders (p= 0.695). The RR in non-avid tumor pts was 20% (1/5 pts). Conclusions.Our study suggests that in advanced gastric cancer pts with FDG-avid tumor the PET predicts objective response at day 42, but not at day 21. A PET response assessment can provide an opportunity to change the treatment in non-responder pts. Prospective trials defining the role of PET in gastric cancer are warranted. No significant financial relationships to disclose.