"She does not plan to seek re-election in 2008," said the spokesman, Len Sistek.
Carson, 69, was hospitalized for about a week in late September for a deep infection near where a leg vein was removed in 1997 when she underwent double heart bypass surgery.
She was still recuperating from that ailment and had not yet returned to Washington when "`the second shoe fell - heavily," Carson said in a statement to The Indianapolis Star Sunday. "My doctor discovered lung cancer. It had gone into remission years before, but it was back with a terminal vengeance."
Carson did not disclose the date of her initial lung cancer diagnosis.
Sistek said he could not discuss Carson's health.
Over the years, Carson has suffered from high blood pressure, asthma and diabetes. She spent the weekend before the 2004 election in the hospital for what she said was a flu shot reaction - but still won re-election by 10 percentage points.
She became the first black and first woman to represent Indianapolis in Congress when she was elected from the predominantly Democratic 7th District in 1996. Carson has championed children's issues, women's rights and efforts to reduce homelessness and has been a staunch opponent of the war in Iraq.
She began her political career in the 1960s when then-Rep. Andy Jacobs Jr. hired her to work in his office. It was Jacobs who encouraged Carson to run for the Indiana Legislature in 1972 - the first of more than two dozen victories in local, legislative and congressional elections. She ran for Congress in 1996 after Jacobs decided to retire.