Shares of Prothena (PRTA) tumbled 22.5% in after-hours trading on May 23 after it announced the discontinuation of the development of the pipeline candidate, birtamimab.The decision to discontinue comes after the late-stage AFFIRM-AL clinical study evaluating birtamimab in patients with AL amyloidosis did not meet its primary endpoint.The company’s shares have lost 52.5% year to date compared with the industry’s decline of 5%.Image Source: Zacks Investment ResearchMore on PRTA’s BirtamimabBirtamimab was a w ...