U.S. Supreme Court Justice Stephen Breyer may have to sit out a high-stakes patent case Wednesday, thanks to a belated disclosure that one of the parties has a new corporate owner.

The Supreme Court has been preparing to hear arguments in a case involving Prometheus Laboratories Inc. that examines whether companies and inventors should be allowed to patent medical diagnostic tests, a key legal question in the growing field of personalized medicine.

Prometheus on Tuesday informed the court that it has been acquired by a subsidiary of Nestle S.A. According to Justice Breyer's most recent financial disclosure report, he owns shares of Nestle. In general, justices recuse themselves from cases in which they have a financial interest in one of the litigants.

A court spokeswoman had no immediate comment on whether Justice Breyer still holds the stock or what he might do in response to the Prometheus disclosure.

If Justice Breyer still owns Nestle shares, it's possible he could sell them and still participate in the court's deliberations.

When the case first arrived at the court, Prometheus was a privately held company. It became a Nestle subsidiary in July. After the Nestle transaction closed, Prometheus did not file a new corporate disclosure statement with the Supreme Court informing the justices of the change in ownership.

A lawyer for the company confirmed that he provided the court with the information Tuesday, but otherwise declined to comment.

Breyer's absence could change the complexion of the case. In a 2006 dissent, he questioned the validity of certain types of diagnostic-test patents. His dissent criticized the high court for dismissing a case that raised the issue without announcing a decision.

The Prometheus case, which gives the court a second chance to rule on the issue, pits doctors and hospitals against the biotechnology and pharmaceutical industries.

Companies are patenting more tests that help doctors set drug dosages or determine whether a person can benefit from a particular treatment. Screening tests that identify people's risk factors for disease also are getting patented more frequently.

Leading medical groups argue that many of the new patents run afoul of prohibitions on patenting abstract ideas or laws of nature. They say patents like Prometheus's could impede the practice of medicine and raise the costs of medical treatment.

Biotech and drug companies say patents on diagnostic tests have spurred advances in personalized medicine, or tailoring treatments to a person's unique biology. They say disallowing the patents could discourage investment and stall progress.

At issue are two Prometheus patents for a test that helps doctors set drug dosages for patients with Crohn's disease.

The company filed a patent-infringement lawsuit against the Mayo Clinic, which wants to offer its own test. The clinic is arguing to the Supreme Court that Prometheus improperly seeks to claim a patent monopoly on the right to observe a natural phenomenon.

A federal trial judge in California ruled the Prometheus patents invalid, but they were reinstated by a special appeals court in Washington.

If the Supreme Court were to split 4-4 in the case, the appeals court ruling for Prometheus would be affirmed.

Thousands of patents for diagnostic tests have been issued over the last two decades and could be affected by the court's ruling.

The case is Mayo Collaborative Services v. Prometheus Laboratories Inc., 10-1150. A ruling is expected by the end of June.