There's more turmoil to report at struggling XBiotech (XBIT) - Get Report . The biotech company's No. 2 executive resigned last week.

Kelly Thornburg, XBiotech's senior vice president of operations, submitted his resignation letter on May 5 and left the company immediately. Thornburg's exit was disclosed in a note at the bottom of the XBiotech 10-Q filed with the Securities and Exchange Commission on Wednesday night.

XBiotech offered no reason for Thornburg's resignation, but he left two weeks after European regulators issued a preliminary recommendation to reject the marketing application for the company's colon cancer drug Xilonix.

In April, a different antibody designed by XBiotech to treat serious staph infections failed to reduce to risk of adverse events or reduce the length of hospitalization stays compared to a placebo. Four patients treated with the antibody died.

Thornburg was a named executive at XBiotech and the second highest-paid employee behind CEO John Simard. Thornburg joined XBiotech in June 2015 after 16 years at Amgen. His expertise is in pharmaceutical operations and drug manufacturing.

A press release announcing Thornburg's hiring in June 2015 emphasized Thornburg's manufacturing expertise, especially as it related to working with regulators to get drugs approved. Thornburg was supposed to help XBiotech transform from a research to a commercial company. His resignation -- and the quiet way XBiotech disclosed it -- suggests that plan has hit a wall.

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