In DCIS, abnormal cells multiply and form a growth within a breast milk duct .

CNN: Martina Navratilova has breast cancer

DCIS, as the cancer is commonly called, has a 95 percent survival rate, Navratilova said.

CNN: Martina Navratilova has breast cancer

Six remained on active surveillance with no evidence their DCIS had worsened.

WSJ: Can Breast Cancer Be Overtreated?

If left untreated, about 30 percent of women with DCIS will develop invasive breast cancer an average of 10 years from the initial occurrence, the Breast Cancer Network of Strength says on its Web site.

CNN: Martina Navratilova has breast cancer

Even in the precancerous stage, called ductal carcinoma in situ (DCIS) when abnormal cells are confined to a milk duct, physicians almost always advise women to have a lumpectomy or mastectomy along with radiation, because about 20% of the 65, 000 cases of DCIS found every year in the U.S. become invasive cancer.

WSJ: Can Breast Cancer Be Overtreated?

The authors, from the University of California, San Francisco, noted that even when DCIS becomes an invasive cancer, it's treatable when found at an early stage: The odds that a 60-year old woman with a 7 millimeter breast tumor, would die from it in the next 10 years are less than 3%, half the risk she faces of dying from another cause during that time.

WSJ: Can Breast Cancer Be Overtreated?