Women with ductal breast cancer in situ were more than five times more likely to be survivors compared with women diagnosed with lobular breast cancer in situ, the Wisconsin researchers found.
In addition, more white women survived than black women and women from other ethnic groups, the researchers found.
Sprague and Trentham-Dietz also found that survival has increased over time. For example, 21,654 women diagnosed in 1975 were still alive in 2005, while that number quadrupled for women diagnosed in 1985 and doubled again for women diagnosed in 1995.
"Assuming constant incidence and survival rates, the estimated prevalence of breast cancer in situ will exceed 1 million cases by 2016," the authors wrote.
Improved survival may be due in part to better screening and earlier diagnosis, the researchers noted. Before 1990, breast cancer in situ made up only 4 percent of all breast cancer diagnoses.
"If there is an underlying increase in in situ breast cancers that is not the result of screening -- and there seems to be -- we should be looking for the causes -- very likely environmental -- of that increase," Brenner said.
The researchers agreed that there is still a lot more to learn about in situ breast cancer.
"Current epidemiologic evidence regarding predictors of subsequent invasive breast cancer after breast cancer in situ is limited," Sprague and Trentham-Dietz wrote. "Guidelines are necessary to help the increasing number of breast cancer in situ survivors choose the best treatment and lifestyle strategies while still maintaining high quality of life."
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