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Can Breast Cancer Disappear?

Study Shows Some Cancers Detected by Mammograms Regress on Their Own; American Cancer Society Disagrees
By
WebMD Health News
Reviewed by Louise Chang, MD

Nov. 24, 2008 -- Can breast cancer disappear? The question may sound ridiculous, but some breast cancers detected on mammography may have spontaneously disappeared if they had not been found and treated, according to a team of researchers from Norway and Dartmouth Medical School.

But a spokesman for the American Cancer Society calls that conclusion an "overreaching leap in logic" and stresses that the benefits of regular mammograms far outweigh the potential harms.

"Some breast cancers will not continue to behave as cancers, even though they look like cancer under the microscope, and they grow and reach a size where they can be detected on mammograms," Jan Maehlen, MD, PhD, a study co-author, tells WebMD. "But if they had been left intact [instead of treated after detection], some will stop growing and shrink and disappear over a course of perhaps two years."

He calls these growths "pseudo-cancers." Even so, Maehlen says, "the message for women is go to screening."

In the study, published in the Archives of Internal Medicine, Maehlen's team looked at breast cancer rates among women in Norway, all ages 50 to 64, who had a single mammogram or three mammograms.

The multiple-screened group included nearly 120,000 women, screened three times between the years 1996 and 2001. The comparison group included nearly 110,000 women, screened once at the end of the observation period.

After the final screening, breast cancer rates were 22% higher in the multiple-screened group. While 1,909 of every 100,000 women in the multiple-screened group had breast cancer, 1,564 of every 100,000 women in the comparison group screened only once did.

Breast Cancer Screening

Maehlen's team concludes that some breast cancers detected by repeat mammograms would not persist at the end of six years, because the total incidence of breast cancer among the comparison group never equaled that of the regularly screened group.

"Breast cancer screening is a two-sided sword," Maehlen says. "Our results shift the balance towards harm and away from benefits. On one hand, a malignant tumor may be detected and treated somewhat earlier and this may decrease the risk to die by a few percent. On the other hand there is a considerable risk that a screening-detected lesion is a pseudo cancer."

He says the results imply that as many as two out of three screenings detected lesions -- including invasive cancers and the noninvasive ductal carcinoma in situ (DCIS) -- may be pseudo cancers.

Maehlen expects the conclusion to spark debate. "The majority of the people in the field would be skeptical," he says.

As to which women might be more likely to have breast cancers that spontaneously regress, Maehlen says that is not known. "It could be the immune system is the cause for the disappearance of some cancers," he says, presumably with the healthiest immune systems most likely to fight off cancers.

Or, he says, it could depend on the biology of the individual cancer as to whether it regresses.

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