"I hope before too long to be sharing news of my good health and recovery," said actress Dana Reeve, 44, who won worldwide admiration for the steadfast support of her husband during his nine years as a quadriplegic.
Christopher Reeve, the star of the "Superman" movies, died last year.
Dana Reeve's announcement came two days after the lung cancer death of ABC News anchor Peter Jennings, a smoker, at age 67.
The Christopher Reeve Paralysis Foundation would not comment on the extent of Reeve's cancer or whether it is restricting her activities. Reeve said it was diagnosed recently and is being treated.
"Dana will tackle this challenge with the grace, courage, and determination that have become her hallmark," said Kathy Lewis, the foundation's president and chief executive officer.
CBS News Correspondent Elizabeth Kaledin reports that Reeve's is one of those rare cases of lung cancer in people who've never smoked. Doctors say only ten percent of non-smoking women and up to 20 percent of non-smoking men get the disease.
In a cancer that is notoriously difficult to treat, that can actually be good news.
"What we do know is that for women with lung cancer who were never smokers they seem to do better," said Ronald Blum of Beth Israel Medical Center.
A month ago, Reeve cited "family reasons" when she canceled an appearance in Washington with actor Michael J. Fox in support of embryonic stem cell research. Christopher Reeve's spinal cord injury, suffered in a fall from a horse, is among the conditions for which such research holds the promise of a cure.
Comedian Robin Williams, a close friend of the Reeves, issued a statement with his wife, Marsha, sending "all of our love and support to Dana and her family during this challenging time."
In her statement, Reeve requested privacy and said she was disclosing the illness only because a tabloid was about to do so.
"More than ever, I feel Chris with me as I face this challenge," she said. "As always, I look to him as the ultimate example of defying the odds with strength, courage and hope in the face of life's adversities."
Reeve did not disclose where she is being treated.
Dr. Scott Swanson, chief of thoracic surgery at Mount Sinai Medical Center in Manhattan, said that depending on the extent of Reeve's cancer, she would be treated with surgery, chemotherapy, radiation or a combination.
Survival rates, he said, are 75 percent for stage 1, where the cancer has barely spread; 50 percent for stage 2, where it is still limited to the lung; 25 percent for stage 3, where the cancer has gotten into the chest; and less than 5 percent for stage 4, where the cancer has spread elsewhere in the body.
He said researchers have noted an increase in lung cancer in nonsmoking women under age 51 and are trying to find the cause.
Reeve, who lives in Pound Ridge in Westchester County with the couple's 13-year-old son, Will, has appeared on Broadway, Off-Broadway and regional stages and on the TV shows "Law & Order," "Oz," and "All My Children." In an Associated Press interview a month after her husband's death, she said, "I am an actress and I do have to make a living. ... I definitely will be getting back to acting."