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ORLANDO, Fla. — Researchers presented early-phase trial results on RLY-2608, Relay Therapeutics’ next-generation PI3K inhibitor, at the American Association for Cancer Research annual meeting on Tuesday. Then Relay’s stock plummeted 36%, leaving some cancer researchers scratching their heads as to why, exactly.

The investigational drug inhibits a protein called PI3K, which is part of a pathway involved in regulating cell growth and division. It’s implicated in a wide variety of cancers, and about 30% of breast cancers have PI3K mutations. There is a drug targeting PI3K, Novartis’ alpelisib, which the Food and Drug Administration approved in 2019. Alpelisib can slow the rate of progression of metastatic breast cancer with PI3K mutations, but toxicity can be brutal on patients.


“They’re really difficult. Hyperglycemia and rash and diarrhea,” said Cynthia Ma, a breast cancer researcher and physician at Washington University in St. Louis who did not work on RLY-2608. “So many patients go off treatment because of side effects.”

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