Health care stocks added to their prior gains this afternoon, with the NYSE Health Care Index rising 1.6% and the SPDR Health Care Select Sector ETF (XLV) up 2.2%. The Nasdaq Biotechnology index also was climbing 3.6%. In company news, Radius Health (RDUS) gained almost 20% after agreeing to an $890 million private-equity buyout offer for biopharmaceutical firm from Gurnet Point Capital and Patient Square Capital.