Centene’s stock suffers a historic plunge as underestimation of healthcare costs leads the insurer to withdraw its full-year earnings outlook.

Centene shares tumbled 38% on Wednesday, on track for their largest single-day plunge, after the U.S. health insurer pulled its 2025 earnings forecast due to an expected slump in revenue from commercial plans under Obamacare.

The health-insurance provider is reckoning with multiple threats to its business, potentially leaving it with fewer and less-healthy enrollees signed up to its health-insurance plans.