Harpoon Therapeutics (NASDAQ:HARP), a biotechnology company developing an antibody platform to treat different forms of cancer, climbed approximately 20% in the last 10 minutes of trading on Friday, May 29, to close at $21.76 per share.

Earlier in the day, Harpoon disclosed respectable but not spectacular phase I results of its antibody drug HPN424.

On April 15, 2019, SanaCurrents assigned a pivotal sentiment phase I results would be positive. At the time of the report, Harpoon traded at $12.73 per share. Harpoon shares climbed to $25.02 per share on May 26 before tumbling the next three days to open at $19.60 per share on Friday. The stock slid further during the day to a low of $16.34 per share before the late rally.

Harpoon held a conference call at the close of trading (4 pm, Eastern) to explain the data released early in the day. The company presentation clarified HPN424 delivered long-term improvement at 2 different doses to very sick patients. While the exact reason for the late surge is not public, the company’s clarification may have become understood by certain investors in the last hour of trading.

A trade on Friday at the opening of the market would have yielded a return of 53%, based on an investment at the time of the report. Holding on to the stock until the market close, or trading early on June 1, would deliver a return 70%.