Tenet Healthcare Corp. THC, -0.26% shares dropped in the extended session Thursday after the hospital operator forecast an outlook that came up short of Wall Street expectations while announcing a share buyback program. Tenet shares fell 21% after hours, following a 0.2% decline in the regular session to close at $54.32. Tenet forecast adjusted earnings of $1 to $1.54 a share on revenue of $4.82 billion to $5.02 billion for the fourth quarter, and $5.88 to $6.42 a share on revenue of $19 billion to $19.2 billion for the year. Analysts surveyed by FactSet had estimated $1.80 a share on revenue of $5.04 billion for the fourth quarter, and $6.38 a share on revenue of $19.27 billion for the year. The company reported third-quarter net income of $131 million, or $1.16 a share, compared with $449 million, or $4.13 a share, in the year-ago period. Adjusted earnings, which exclude stock-based compensation expenses and other items, were $1.44 a share, compared with $1.99 a share in the year-ago period. Revenue declined to $4.8 billion from $4.89 billion in the year-ago quarter. Analysts had forecast $1.24 a share on revenue of $4.81 billion. Tenet also announced a $1 billion share-buyback program.