Health care stocks were mixed premarket Monday, with the Health Care Select Sector SPDR Fund (XLV) down 0.2% and the iShares Biotechnology ETF (IBB) 0.5% higher.

Metsera (MTSR) announced late Friday an amended merger deal, under which Pfizer (PFE) will acquire Metsera for up to $86.25 per share. Metsera's board determined that the revised terms represent the "best transaction" for shareholders and that the deal proposed by Novo Nordisk (NVO) presents "unacceptably high legal and regulatory risks." Metsera shares were down more than 15% pre-bell.

Immunovant (IMVT) shares were down more than 5% after the company reported a narrower fiscal Q2 net loss that still missed analysts' expectations.

Revvity (RVTY) stock was up more than 1% after the company said it has entered into a definitive agreement to acquire ACD/Labs.