By Michael Dabaie 



  Surface Oncology shares continued the previous day's gains in Thursday morning trading, recently up 45% to $5.61. 


  Surface Wednesday said it entered into a clinical trial collaboration with Merck & Co., through a subsidiary, to evaluate combining Surface's SRF617 with Merck's Keytruda. 


  The combination will be studied as a component of a Phase 1/1b study of SRF617 and will be evaluated in patients with solid tumors, with a focus on patients with gastric cancer and those who have developed resistance to checkpoint inhibition, areas of high unmet need, Surface said. 


  Surface also said Wednesday that it raised gross proceeds of about $28.9 million through its at-the-market facility. 


  Write to Michael Dabaie at michael.dabaie@wsj.com