Shares of the Austin company at last check were down 3.8% to $55.01.
Cassava, which announced the study in February, said the initial Phase 3 study is designed to evaluate the safety and efficacy of simufilam in enhancing cognition and slowing cognitive and functional decline over 52 weeks.
The study's secondary objectives include assessing simufilam's effect on neuropsychiatric symptoms and caregiver burden.
The double-blind, placebo-controlled study plans to enroll roughly 750 patients with mild-to-moderate Alzheimer’s disease in the U.S. and Canada and, eventually, overseas.
Cassava said that a second Phase 3 study of the drug is expected to begin by the end of the year.
The company became embroiled in controversy in August when Jordan Thomas, a partner and chair of the whistleblower representation practice at Labaton Sucharow, filed a Citizen's Petition with the U.S. Food and Drug Administration seeking a halt to trials of simufilam.
Thomas, a former Security and Exchange Commission enforcement lawyer who helped set up the agency’s whistleblower program, raised concerns about "the quality and integrity of the laboratory-based studies surrounding this drug candidate."
Cassava, which had earlier reported progress in a study of the drug. labeled the allegations as "fiction."
The issue became more complicated after the diagnostics company Quanterix (QTRX) - Get Quanterix Corporation Report said it didn't interpret test results or prepare data charts about simufilam that Cassava presented at the Alzheimer’s Association International Conference in July.
Cassava Sciences said Quanterix conducted sample testing, then sent the raw data to the company for analysis of treatment effects.
Last month, B. Riley analyst Mayank Mamtani reiterated his buy rating on Cassava Sciences with a $108 price target.
The analyst said the company's readout from a pre-planned 12-month treatment interim analysis of its ongoing open-label trial evaluating simufilam reinvigorated investor confidence.
While this cognition data update and evaluation methodology "to some extent, helps assuage investor concerns" emanating from the Citizen's Petition, the analyst said Cassava needs supportive 12-month biomarker analyses.