Merck & Co. is reportedly in talks to acquire Prometheus Biosciences Inc.

The talks are said to be in the late stage with a deal possibly announced as soon as Sunday, according to The Wall Street Journal.

A deal is not certain and could still fall apart.

The deal could give Merck promising immune disease treatments.

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FOX Business has reached out to Merck and Prometheus Biosciences for comment.

Prometheus had a market cap of $5.4 billion as of Friday’s market close. Its shares are up about 4% year-to-date.

Merck is looking to add new products to its pipeline as its top-selling drug cancer therapy Keytruda, is expected to lose patent protection this decade.

Merck’s sales last year came to $59.3 billion, with Keytruda sales making up roughly $21 billion of it.

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The San Diego-based Prometheus develops immune treatments and doesn’t have any approved products.

The company's pipeline drug in development treats immune diseases including ulcerative colitis and Crohn’s disease and recently reported separate positive study results in mid-stage testing.

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Company sales totaled $6.8 million last year.

Merck recently made another deal, agreeing to acquire blood-cancer biotech Imago BioSciences for $1.35 billion.