John Milligan will step down as president and CEO of Gilead Sciences (NASDAQ: GILD) at the end of the year, the Foster City, CA company announced Wednesday. Milligan’s departure will end a 28-year career with the company. In a prepared statement, Milligan said he would move on to “new and different opportunities.” Milligan will also leave his seat on Gilead’s board of directors. A search for Milligan’s successor is underway. Gilead also announced that board chairman John Martin will step down. Martin will leave the board when a new CEO joins Gilead.