Quest Diagnostics, a leading medical lab testing company, confirmed that a recent cyberattack compromised sensitive patient information stored on its lab testing system called Quanum. The breach was disclosed in an 8-K filing with the U.S. Securities and Exchange Commission, revealing that unauthorized access occurred on Wednesday and affected patient health and billing data. Quest is investigating the incident and has informed law enforcement as it works to understand the full scope of the breached data.

The Quanum platform is widely used, serving around half a million clinicians across thousands of healthcare locations in North America. While Quest has not yet specified how many patients or records were involved, the system holds substantial amounts of personal and medical data, including diagnostic results and billing information. The company’s security notice states that protected health information was accessed, though exact details on the data stolen remain under investigation.

This breach is the latest in a troubling pattern of cyberattacks on the healthcare sector in 2026. Other major incidents this year include disruptions at medical device firms Stryker and Boston Scientific, as well as data thefts from companies like CareCloud, Craneware, and McKesson. Cybercriminals continue to target health technology firms for the lucrative and sensitive data they hold, often threatening to release stolen records if ransoms are not paid.

Quest Diagnostics previously experienced a significant breach in 2019 when nearly 12 million patient records were exposed through a third-party billing provider cyberattack. The company has not disclosed whether ransom demands have been made in the current case or when the compromise initially began. Quest spokesperson Amanda Rivera directed inquiries to the company’s security notice but provided no additional comment, leaving details and impact assessment ongoing.