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."
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.
The American Cancer Society took issue with the thinking that cancer may regress on its own. "The conclusion that more than 1 in 5 invasive breast cancers is destined to regress without incident if not detected by mammography [the 22% figure cited in the study] is nothing more than an overreaching leap in logic," Robert A. Smith, PhD, director of cancer screening for the American Cancer Society, says in a prepared statement.
Other studies have found that "overdiagnosis" -- not the same as regression -- probably occurs in less than 5% of all screen-detected cancer cases if it exists at all, Smith says.
He says the benefits of regular mammograms far outweigh any limitations, such as false-positive results and "possibly a small rate of overdiagnosis."
The study has weaknesses, but also strengths, says Robert Kaplan, PhD, the Wasserman Distinguished Professor and chair of the department of health services at the University of California, Los Angeles School of Public Health, in an editorial accompanying the study.
As a result, he writes, "the findings should not be dismissed."
The study, Kaplan says, points out how little experts know about the natural history of breast cancer.
The concept of breast cancer spontaneously regressing is worth further study, Kaplan writes.