Breast cancer screening false positive results may need more follow up: Study

By Dr. Ananya Mandal, MDApr 5 2012

According to a new study false positive results in breast cancer screenings might not be so benign after all.

A Danish study of more than 58,000 women found those who had false positive mammograms, meaning the results suggested breast cancer when there was none, had a 67 percent higher risk of developing breast cancer later in life compared with women who had negative mammograms.

“The excess breast cancer risk in women with false-positive tests may be attributable to misclassification of malignancies already present at the baseline assessment ... or to a biological susceptibility for developing breast cancer in some women without malignancies at baseline,” the study authors wrote, describing how dense, irregular breast tissue may disguise or develop into cancer. The study was published today in the Journal of the National Cancer Institute.

The U.S. Preventive Services Task Force recommends biennial mammograms for women between the ages of 50 and 74. Mammograms can also lead to false positives, prompting unnecessary tests and procedures, not to mention anxiety. It's estimated that for one woman's life to be saved through mammography, 2,000 women have to be screened and 200 will get a false positive. False positives usually lead to biopsies, which remove a tiny piece of the questionable tissue for further tests. But 10 of 200 women with false positives will undergo unnecessary surgery.

But Dr. Susan Love, president of the Dr. Susan Love Research Foundation, said women who have a family history of breast cancer are more likely to have a false positive. “It so subjective,” she said of a radiologist's decision to follow up a suspicious mammogram with a biopsy. “If you had a mother with breast cancer, the radiologist and ... probably you yourself would be more aggressive in following up any slightly suspicious abnormality in a screening mammogram.”

But there are other, more biological explanations, too. “Surgery or needle biopsies may cause a local inflammatory or wound-healing reaction, which increases cancer risk,” or “the extra radiation from the workup for the false positive could increase breast cancer,” explained Love. “Or we might be picking up on some subtle change in the microenvironment, the fibrous tissue, that's more conducive to cancer growing. We just don't know.”

Dr. Marisa Weiss, president of BreastCancer.org, said American doctors would almost always follow up on suspicious mammogram results out of fear of litigation. “The biopsy rate is higher here than in places like Denmark,” she said. “We have no tolerance for uncertainty or missed diagnoses.”

Weiss said the Danish study highlighted the importance of routine check-ups after a false positive. “Women who had a false positive still need to be followed carefully over time,” she said. “Even though the last thing you want to do is go back for another mammogram.”

Birth control implants and breast cancer risk

In another study, researchers found that an injectable form of birth control doubles breast cancer risk among young women.

The study examined younger women, ages 20 to 44, and confirmed a link between depo-medroxyprogesterone acetate (DMPA) - the main ingredient in the contraceptive sold under the brand name Depo-Provera - and breast cancer risk. The contraceptive shot is usually injected into the buttocks or upper arm once every 3 months, or just under the skin once every 12 to 14 weeks.

Researchers say few studies have examined the link between DMPA and breast cancer risk, and this is the first large scale U.S. study to do so. The study, led by researchers at the Fred Hutchinson Cancer Research Center in Seattle, is published in the April 15 issue of Cancer Research.

The research involved over 1,000 young women diagnosed with breast cancer. About 10 percent of those women reported using DMPA, which study authors say is consistent with nationwide usage patterns.

Women who had used DMPA for at least one year had a risk for breast cancer 2.2 times greater than those who did not use the injectable birth control. Women who had used DMPA for less than a year or had stopped using it more than a year ago did not have an increased risk, meaning discontinuing use may be effective.

Lead author Dr. Christopher Li of Fred Hutchinson Cancer Research Center in Seattle, Wash. said in a statement, “In the United States many women have numerous options for contraception, and so it is important to balance their risks and benefits when making contraceptive choices.”

“Although breast cancer is rare among young women and the elevated risk of breast cancer associated with DMPA appears to dissipate after discontinuation of use, our findings emphasize the importance of identifying the potential risks associated with specific forms of contraceptives given the number of available alternatives,” the authors wrote in a news release.