Health care stocks edged up late Thursday afternoon, with the NYSE Health Care Index and the Health Care Select Sector SPDR Fund (XLV) each adding less than 0.1%.

The iShares Biotechnology ETF (IBB) decreased 0.7%.

In corporate news, Day One Biopharmaceuticals (DAWN) has agreed to buy Mersana Therapeutics (MRSN) in a deal valued at up to about $285 million. Mersana shares surged 210%.

Pfizer (PFE) shares were down 0.4% after it said Thursday it has completed its acquisition of Metsera (MTSR) for about $7 billion in cash plus a contingent value right of up to $20.65 per share tied to the achievement of three specified clinical and regulatory milestones.

BioNTech's (BNTX) collaboration with Pfizer has not changed, Reuters reported Thursday, citing a BioNTech spokesperson who was asked to comment on a media report saying Pfizer may sell its stake in the German biotech company. BioNTech shares were falling 6.8%.

Novo Nordisk (NVO) raised 4 billion euros ($4.7 billion) in a bond sale to help finance its planned acquisition of Akero Therapeutics (AKRO), Bloomberg reported. Novo shares were down 2.5%.