Pfizer Inc. /zigman2/quotes/202877789/composite PFE -0.49% has reached an agreement to buy Global Blood Therapeutics Inc. [s :gbt] in a deal valued at $5.4 billion, the Wall Street Journal reported, citing people familiar with the matter. The news comes after the Journal reported Friday that the two were in advanced talks. Pfizer will pay $68.50- a share in cash for Global Blood Therapeutics, which has one of few approved treatments for sickle-cell disease. The companies are expected to announce the deal later Monday. Global Blood Therapeutics shares rose 1.8% in premarket trade Monday, and are up 118% in the year to date, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.23% has fallen 13%.