Efficacy of trastuzumab emtansine in Japanese patients with previously treated HER2-positive locally advanced or metastatic gastric or gastroesophageal junction adenocarcinoma: A subgroup analysis of the GATSBY study.

The phase II/III GATSBY study (NCT01641939) showed that trastuzumab emtansine did not have an efficacy benefit over taxane in patients with previously treated, human epidermal growth factor receptor 2 (HER2)-positive advanced or metastatic gastric or gastroesophageal junction cancer. We evaluated patients from Japanese centers within GATSBY. In stage one, patients (randomized 2:2:1) received trastuzumab emtansine 3.6 mg/kg every 3 weeks, trastuzumab emtansine 2.4 mg/kg weekly, or physician's choice of taxane (docetaxel 75 mg/m² every 3 weeks or paclitaxel 80 mg/m² weekly). In stage two, patients (randomized 2:1) received trastuzumab emtansine 2.4 mg/kg weekly or taxane. Eligible patients had centrally assessed HER2-positive disease and progression during or after first-line therapy. Primary endpoint was overall survival. We present the 2.4 mg/kg weekly data. Eighty-two patients were randomized (intention-to-treat: 48 to trastuzumab emtansine 2.4 mg/kg weekly, 23 to taxane; September 2012-August 2014) at 19 sites. Median overall survival was 11.8 months (95% confidence interval [CI], 9.3-16.3) with trastuzumab emtansine 2.4 mg/kg weekly and 10.0 months (95% CI, 7.1-18.2) with taxane (unstratified hazard ratio = 0.94, 95% CI, 0.52-1.72). Trastuzumab emtansine 2.4 mg/kg weekly, versus taxane, was associated with fewer grade ≥3 adverse events (AEs; 52.1% vs 68.2%) and serious AEs (14.6% vs 18.2%). There were no fatal AEs. Efficacy in Japanese patients within GATSBY was consistent with the overall population; overall survival was not prolonged with trastuzumab emtansine 2.4 mg/kg weekly versus taxane. The safety profile of trastuzumab emtansine was similar to the overall population.

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