Biomarker analysis of the GATSBY study of trastuzumab emtansine versus a taxane in previously treated HER2-positive advanced gastric/gastroesophageal junction cancer

摘要

BackgroundPrespecified exploratory biomarker analyses of the phase II/III GATSBY study (NCT01641939) assessed whether patient subgroups experienced a survival benefit from trastuzumab emtansine (T-DM1) versus taxane therapy, and to advance understanding of HER2-positive advanced gastric/gastroesophageal junction cancer (AGC) disease biology.MethodsAdults with HER2-positive AGC whose disease progressed during/after first-line therapy were enrolled and randomized to receive T-DM1 [Stage 1: 3.6mg/kg q3w, 2.4mg/kg qw, or taxane (docetaxel/paclitaxel); Stage 2: 2.4mg/kg qw or taxane]. Primary efficacy endpoint was overall survival (OS). Prespecified exploratory biomarkers included HER2, HER3, PTEN, PIK3CA mutation status, FcR, and cMET. Tumor samples from patients who received 2.4mg/kg T-DM1 (n=228) or taxane (n=117) were included.ResultsMedian OS was longer in subgroups with HER2 immunohistochemistry (IHC) 3+ [9.5 versus 8.3 months for T-DM1 versus taxane; hazard ratio (HR) 0.99 (95% CI 0.68-1.43)] versus HER2 IHC 2+/in situ hybridization-positive [5.2 versus 9.2 months for T-DM1 versus taxane; HR 1.53 (95% CI 0.94-2.50)] tumors. Trends towards increased median OS were also observed in subgroups with >versus median HER2 mRNA expression, higher versus lower HER2 gene copy number, HER2 gene ratio and H score, and homogenous or nonfocal HER2 IHC staining. T-DM1 was not associated with superior OS versus taxane in any subgroup.ConclusionsPatients with previously treated HER2-positive AGC with higher HER2 expression experienced a better treatment effect from T-DM1 than those with lower HER2 expression and may derive comparable survival benefits from T-DM1 and taxane therapy.Clinical trials registrationNCT01641939 (https://clinicaltrials.gov/ct2/show/NCT01641939).