Mammographic screening has also increased the diagnosis of noninvasive cancers and premalignant lesions.

In cases of noninvasive cancers, simple mastectomies are performed in which only the breast with the lining over the chest muscles are removed.

Although some of these very early noninvasive cancers may never become invasive and life-threatening, it is not possible to predict which will remain nonthreatening.

Such noninvasive intraductal cancers account for only about 5 percent of breast cancers.

If it hasn't broken through, though, it's called in situ, or noninvasive cancer.

Nonetheless, the risk of developing noninvasive cancer increases with age and it is higher in women older than 45 years.

Lumpectomies are commonly performed with radiation therapy to avoid noninvasive cancer from recurring or from developing into invasive cancers.

With the increasing use of screening mammography, noninvasive cancers are more frequently diagnosed and now constitute 15% to 20% of all breast cancers.

D.C.I.S., which is also called Stage 0 or noninvasive cancer, was a rare diagnosis before mammograms began to be widely used in the 1980s.