(Bloomberg) — Cassava Sciences Inc. plummeted as much 29% on Friday after a lab denied it had prepared recent results for the biotech’s lead product, an experimental Alzheimer’s disease treatment.

The denial counters a Wednesday statement from the company that Quanterix Corp. generated the results. Cassava shares have fallen about 50%, shaving off roughly $2.5 billion of value over the past three trading days. The fall comes after a former Securities and Exchange Commission lawyer petitioned the U.S. Food and Drug Administration to put a halt to Cassava’s trials of the drug on questions over the integrity of the results.

Quanterix said it had performed some prior services to Cassava but “Quanterix or its employees did not interpret the test results or prepare the data charts presented by Cassava at the Alzheimer’s Association International Conference (AAIC) in July 2021 or otherwise,” according to a company statement.

Cassava didn’t immediately respond to requests for comment.

The stock is still one of the best performers this year second only to AMC Entertainment Holdings Inc. among Russell 2000 Index members. The Austin, Texas-based company’s more than 700% rally was fueled by the approval of Biogen Inc.’s Aduhelm — the first new Alzheimer’s disease treatment in over a decade — as well as the recent retail trading frenzy.

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