BOSTON (Reuters) - Representative Stephen Lynch, a Massachusetts Democrat who has represented Boston and its surrounding since 2001, on Thursday formally launched a bid for the U.S. Senate, seeking the seat being vacated by John Kerry following his confirmation as the new U.S. secretary of state. Lynch, a former ironworker, will face off against fellow House of Representatives member Edward Markey in an April 30 primary, ahead of a June 25 special election to choose a permanent successor to Kerry. ...