Tennis great Martina Navratilova has been diagnosed with a non-invasive form of breast cancer and her prognosis is considered excellent.

Navratilova said April 7 that a routine mammogram in January found a lump and a biopsy the following month determined it was ductal carcinoma in situ, or DCIS. The nine-time Wimbledon women's singles champion had a lumpectomy 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."

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 her 50th birthday.