Associations between early tumor shrinkage and depth of response and clinical outcomes in patients treated with 1st-line chemotherapy for advanced gastric cancer.

Background: Although early tumor shrinkage (ETS) predictions of the efficacy and depth of response (DpR) reflects clinical outcomes in chemotherapy with epidermal growth factor receptor inhibitor regimens to treat metastatic colorectal cancer, their value in assessing treatments for advanced gastric cancer (AGC) is unclear. Here we evaluated relationships between ETS and DpR and clinical outcomes in AGC patients treated with first-line chemotherapy.
Methods: We retrospectively enrolled 612 consecutive patients treated with first-line chemotherapy for AGC between January 2010 and June 2016. ETS and DpR were defined as changes from baseline in summed longest diameters in target lesions at 8 (±4) weeks for ETS and at the smallest observed volume for DpR.
Results: Eligible patients were sorted into HER2 ⁺ (n = 100) and HER2 ^- (n = 186) groups. Median follow-up was 14.8 months. The overall response rate and disease control rates were 64 and 87% in the HER2 ⁺ group and 53.2 and 86.0% in the HER2 ^- group. Respective median PFS and OS were HER2 ⁺ : 7.9 and 20.8 months and HER2 ^- : 6.6 and 13.8 months. The respective ETS rate and median DpR were HER2 ⁺ : 70 and 44% and HER2 ^- : 57.5 and 24%. Clinical outcomes and ETS/DpR were correlated, especially in the HER2 ⁺ group (OS: P < 0.0001; PFS: P < 0.0001). In multivariate analysis, ETS was an independent predictor for OS in the HER2 ⁺ group and for PFS in both groups.
Conclusion: These results indicate that ETS may be an early-on treatment predictor of the efficacy of HER2 ⁺ advanced gastric cancer treated with first-line chemotherapy that includes trastuzumab.