MacroGenics Inc. said a combination of its medicine margetuximab with pembrolizumab shrank tumors in a mid-stage gastric cancer study.
Merck & Co. Inc. markets pembrolizumab as Keytruda. The phase 2 trial enrolled patients with advanced HER2 positive gastric or gastroesophageal junction cancer, that has returned or is resistant to treatment with chemotherapy and trastuzumab, which Roche Holding AG markets as Herceptin.
MacroGenics said 32.7%, or 18 of the 55 patients evaluable as of Jan. 8, exhibited objective responses — tumor shrinkages as predefined under the study. The disease control rate, which applies to tumors that showed little to no change, was 69.1%. The median length of time patients survived without their cancer worsening, a measure called progression-free survival, or PFS, was 4.7 months.
Among the 23 patients with tumors bearing the PD-L1 protein, which pembrolizumab blocks from linking up its PD-1 counterpart on a healthy cell, the objective response rate was 52.2%, equal to 12 patients. The disease control rate, at 82.6%, was also higher in this subset of patients. PD-L1 positive patients had a median PFS of 4.14 months.
As of Jan. 8, 13 gastric cancer patients remain on therapy, according to MacroGenics. The median overall survival under treatment with margetuximab and pembrolizumab had not been reached, meaning the length of time in which half of the patients are expected to be alive remains undocumented.
Acceptable tolerability was observed in the safety population of 95 patients, 92 of whom received, every three weeks, margetuximab at 15 milligrams per kilogram and pembrolizumab at 200 milligrams — the trial's recommended dose. Grade 3 or higher treatment-related adverse events occurred in 17.9% of the patients.
Rockville, Md.-based MacroGenics presented the data in a poster session at the 2019 ASCO Gastrointestinal Cancers Symposium in San Francisco.
The company granted Zai Lab Ltd. rights to develop and market margetuximab in Mainland China, Hong Kong, Macau and Taiwan in November 2018. Margetuximab previously received fast-track status from the U.S. Food and Drug Administration, as a treatment for a certain type of breast cancer.