(Reuters) -Merck & Co is in late-stage talks to acquire Prometheus Biosciences Inc to get its hands on promising immune disease treatments, the Wall Street Journal reported on Sunday citing people familiar with the matter.

A deal could be announced as soon as Sunday, the people quoted said, though cautioning the talks could still fall apart.

Prometheus, a clinical-stage biotechnology company specializing in therapeutic products for the treatment of immune-mediated diseases, had a market capitalization of $5.42 billion as of the close on Friday.

Merck has been looking for deals to protect itself from eventual revenue loss as its cancer immunotherapy Keytruda patents begin to expire toward the end of the decade.

Merck in February forecast 2023 earnings below Wall Street estimates and an expected steep decline in sales of its COVID-19 antiviral treatment.

Merck and Prometheus did not immediately respond to a Reuters request for comment.

(Reporting by Kanjyik Ghosh in Bengaluru; Editing by Tom Hogue)