The study, which covered nearly 3,000 women, focused on so-called ductal carcinoma in situ, or DCIS - abnormal cells in the milk ducts that are considered the earliest stage of breast cancer. The most common treatment involves removing only the abnormal tissue and conserves the breast.

But researchers said the findings, which appeared in the Journal of the National Cancer Institute, pointed to a downside of breast-conserving surgery for DCIS.

"Women making treatment decisions about DCIS need to understand that many women will need additional surgery or invasive intervention after breast-conserving surgery," said Joshua Fenton, an assistant professor at the University of California, Davis, who co-wrote an editorial published with the study.

The most common invasive procedure is usually a biopsy to remove abnormal tissue in the same breast.

Of the 2,948 women in the study, all of whom had breast-conserving surgery for DCIS between 1990 and 2001, 41 percent had at least one mammogram to check out symptoms or a suspicious lump. And 66 percent had at least one invasive procedure.

But only eight percent actually had a DCIS recurrence and another eight percent were found to have invasive breast cancer.

Larissa Nekhlyudov at Harvard Medical School and Harvard Vanguard Medical Associates in Boston, who led the study, said women should be aware that breast conserving surgery can come with a long follow-up.

"We're not suggesting that women have a mastectomy instead," she said.

"The good news is that the majority of these women will not have a (cancer) recurrence. But the work-ups for a possible recurrence are likely to continue for years."

The findings fit into the bigger issue of the pros and cons of mammography screening. In the United States, the government-backed U.S. Preventive Services Task Force recommends screening women ages 50 to 74 every other year. Some medical groups, though, call for regular mammograms for all women from age 40.

Since mammograms came into widespread use in the 1980s, the number of DCIS diagnoses has shot up. About one in five newly-diagnosed breast cancers is DCIS.

The problem is that DCIS may or may not progress to tumors that invade the breast tissue, and currently there is no way to predict which cases will progress.

So women with DCIS almost always receive treatment, which for some may be unnecessary.

When it comes to early prostate cancer, which is also usually caught through screening, men have the option to delay treatment and choose "active surveillance" - where the cancer is monitored to see if it's progressing.

That's because prostate cancer is frequently slow-growing and may never threaten a man's life.

But this is not an option for DCIS yet since there's no way of telling which tumors might progress quickly, although it could become one if researchers find certain tumor characteristics that strongly predict it's benign, Fenton said.

This will also probably take a "cultural shift," Nekhlyudov noted, since people typically want aggressive treatment for cancer, even if it's early stage. SOURCE: bit.ly/IEYv3o

(Reporting from New York by Amy Norton at Reuters Health; editing by Elaine Lies and Bob Tourtellotte)

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