Shares of Regeneron Pharmaceuticals Inc. (ticker: REGN) and Summit Therapeutics plc (ticker: SMMT) experienced sharp declines on May 30, 2025, impacting the biotech sector exchange-traded fund SPDR S&P Biotech ETF (ticker: XBI), which is market-cap weighted. REGN's decline of approximately 18.5% has been noted as a drag on the broader biotech index, prompting speculation that the company may need to pursue acquisitions or partnerships to stabilize its position. Summit Therapeutics saw an even steeper drop, with its stock falling between 22% and 30%, closing near $13 per share. The selloff in SMMT followed a near-miss on an overall survival (OS) endpoint in its clinical trial, which some investors initially downplayed. Despite the significant pullback, some analysts emphasize that the setback does not negate the company's one-year gains or the potential of its PD1xVEGF drug candidate, viewing the decline as a typical hurdle in drug development rather than a definitive failure.