A report quoted Navratilova, 53, as saying about the moment in February when a biopsy came back positive after a routine mammogram revealed a cluster in her left breast.
"I cried. It knocked me on my ass, really. I feel so in control of my life and my body, and then this comes, and it's completely out of my hands," she told US online magazine People.
Wednesday's report said she would begin six weeks of radiation therapy in May following minor invasive surgery called a lumpectomy and the prognosis for survival was extremely good.
She was diagnosed with a non-invasive form of breast cancer, the report said, called ductal carcinoma in situ, or DCIS, which in her case had not spread to the breast tissue.
"It was the best-case scenario you could imagine for detecting breast cancer," Mindy Nagle, a good friend of Navratilova, told the magazine.
Shelley Hwang, a breast surgeon at UC San Francisco, said DCIS strikes almost 70,000 American women annually and accounts for about one-fifth of all new diagnosed breast cancers.
"The prognosis of someone with DCIS is excellent," she told the magazine (www.people.com). "There's only a one percent chance anyone with this diagnosis would die of breast cancer."
The nine-times Wimbledon champion, who still plays tennis and ice hockey and competes in triathlons, said she was lucky, as she had not been getting regular check-ups.
"I went four years between mammograms. I let it slide. Everyone gets busy, but don't make excuses. I stay in shape and eat right, and it happened to me. Another year and I could have been in big trouble."
Czech-born Navratilova, who became a US citizen in 1981, won 18 Grand Slam singles crowns.
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