Navratilova said in a phone interview Wednesday that a routine mammogram in January found a lump, and a biopsy the following month determined it was in situ, or DCIS. The nine-time Wimbledon women's singles champion had a in March and will start six weeks of radiation therapy next month.
"It was such a shock for me," Navratilova said. "It was my 9/11."
According to the National Institutes of Health, more than 50,000 women each year are diagnosed with DCIS, in which abnormal cells haven't left the milk duct to penetrate breast tissue. It's removed because it is a risk factor for developing invasive cancer. Only about 2 percent of DCIS patients die of breast cancer in the next 10 years.
People magazine's Web site first reported Navratilova's diagnosis.
Navratilova said she initially wanted to keep her diagnosis quiet, but decided she could help others by going public. She will do a Web chat Thursday in her role as the AARP's Health and Fitness Ambassador, when she hopes not only to teach participants but to learn from them.
Navratilova plans to work as a commentator for the Tennis Channel during the French Open while undergoing radiation therapy in Paris, and she wants to hear from others whether she'll have the energy to do that.
One of the most accomplished tennis players in history and an outspoken voice for social causes, Navratilova won 59 Grand Slam titles overall, including 18 in singles, 31 in doubles and 10 in mixed doubles. The last was a mixed doubles championship with Bob Bryan at the 2006 U.S. Open, a month shy of Navratilova's 50th birthday.
She originally retired in 1994, with a record 167 singles titles and having spent 331 weeks ranked No. 1. She returned to the tour as a doubles player in 2000 and couldn't resist dabbling in singles, including a first-round victory at Wimbledon in 2004.