** Shares of health insurer UnitedHealth UNH.N rise 8.2% to $293.39 in extended trading
** Warren Buffett's Berkshire Hathaway BRKa.N has acquired 5 million shares or 0.55% stake in UNH, according to a regulatory filing
** The investment comes as UnitedHealth faces soaring medical costs and a spate of federal investigations
** Up to last close, stock down 46.3% YTD