Whether women choose a mastectomy or breast-conserving surgery, the prognosis is “excellent,” Fenton said in an email. Nearly all women survive for at least five years, he noted.

But that means that other factors, like the need for follow-up procedures, have to be considered, according to Nekhlyudov.

The findings fit into the bigger issue of the pros and cons of mammography screening for breast cancer. 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 starting at age 40.

Since mammography screening came into widespread use in the 1980s, the number of DCIS diagnoses has shot up.

DCIS is almost always caught because of mammography screening, Fenton said, and 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 right now, there’s no way to predict which cases will progress.

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

The new study highlights that treatment does not stop with the initial surgery.

The findings are based on data from 2,948 U.S. women who had breast-conserving surgery for DCIS between 1990 and 2001.

Over 10 years, 41 percent had at least one diagnostic mammogram - one done to check out symptoms or a suspicious lump. And 66 percent had at least one invasive procedure.

However, just eight percent actually had a DCIS recurrence over the years and another eight percent were found to have invasive breast cancer.

It’s not possible to tell whether the women underwent “too many” procedures over time, both Fenton and Nekhlyudov said.

But Fenton pointed out that half of the women had an invasive procedure in the same breast within six months of surgery. Most, he said, were probably re-excisions to ensure that the “margin” around the original tumor was cancer-free.

Studies have found that rates of such re-excisions vary widely from hospital to hospital, and surgeon to surgeon, Fenton said.

“This implies the need for better agreement about when women receiving breast-conserving surgery need additional early surgery,” he said.

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.

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

It will also probably take a “cultural shift,” Nekhlyudov noted, since people typically want aggressive treatment for cancer, even if it’s early-stage.

It’s been estimated that by 2020, one million U.S. women will be living with a diagnosis of DCIS.

SOURCE: Journal of the National Cancer Institute, online April 5, 2012

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