This episode's headline: Pork Progress?; Lung Cancer; Ruling the Range; Conversation. ANCHOR: JIM LEHRER; GUESTS: DR. MARK CLANTON; DR. JOAN SCHILLER; TOM MATHEWS; CORRESPONDENTS: ALEX THOMPSON; KWAME HOLMAN; RAY SUAREZ; SPENCER MICHELS; MARGARET WARNER; GWEN IFILL; TERENCE SMITH; KWAME HOLMAN