Researchers have long known that atypical hyperplasia - an accumulation of abnormal cells in the ducts or lobules of the breast - can increase a woman's risk of breast cancer. But a new study by researchers from the Mayo Clinic finds that this risk may be higher than previously thought.

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Women with atypical hyperplasia have a significantly higher risk of developing breast cancer during their lifetime than women without the condition, according to Mayo Clinic researchers.

According to the research team - led by Dr. Lynn Hartman, an oncologist at the Mayo Clinic - of the more than 1 million biopsies with benign results that are performed in the US each year, atypical hyperplasia is discovered in around 10%.

It is unclear what causes atypical hyperplasia - also referred to as atypia - but it is known that the condition occurs when breast cells become abnormal in terms of size, shape, number, appearance and growth pattern.

Although the condition is not a form of breast cancer, it does incorporate some of the characteristics seen in the early stages of the disease. As such, past studies have indicated that women with atypical hyperplasia may be four to five times more likely to develop breast cancer than those with normal breast cells.

However, Dr. Hartman and her team note that few studies have investigated the "absolute risk" of a woman with atypical hyperplasia developing breast cancer - that is, their likelihood of developing the disease over a specific time period.

Risk of breast cancer increased 1% each year from time of biopsy

With this in mind, the researchers analyzed 698 women who had been diagnosed with atypical hyperplasia after undergoing breast biopsies at the Mayo Clinic between 1967 and 2001.

Fast facts about breast cancer
  • Around 232,670 new cases of breast cancer were diagnosed in the US in 2014
  • Breast cancer is the second leading cause of death in American women
  • There are currently more than 2.8 million breast cancer survivors in the US.

Learn more about breast cancer

The researchers assessed the women's medical records and monitored their atypia pathology. In addition, all women completed follow-up health questionnaires, from which the researchers were able to gather information on any breast cancer diagnoses.

Over an average follow-up period of 12.5 years, 143 women had developed breast cancer.

On analyzing the women's absolute risk of breast cancer from the time of biopsy, they found that it increased by more than 1% each year; 7% of women had developed the disease after 5 years, 13% had developed it after 10 years, while 30% developed breast cancer 25 years after biopsy.

The researchers note that similar results were found in a separate cohort of women with atypia, assessed by investigators from Vanderbilt University in Nashville, TN.

Women with atypia should be recognized as having a high lifetime risk of breast cancer

In addition, the team applied information from patients' pathology specimens to the absolute risk results, with the aim of reaching more accurate risk estimates.

They found that a woman's risk of breast cancer increased along with the intensity of atypia in a patient's biopsy - determined by the amount of separate clusters of abnormal breast cells.

In the case of women with three or more clusters of abnormal breast cells in their biopsies, for example, 47% had developed breast cancer 25 years after biopsy, compared with only 24% of women who had one cluster.

These findings, the researchers say, indicate that women with atypical hyperplasia should be acknowledged as having a high lifetime risk of breast cancer and should undergo regular screening for the disease.

The team also points out that these women should be prescribed anti-estrogen medications - such as tamoxifen - which have been shown to reduce the risk of breast cancer in women with atypia by at least 50%.

Dr. Hartman adds:

"By providing better risk prediction for this group, we can tailor a woman's clinical care to her individual level of risk.

We need to do more for this population of women who are at higher risk, such as providing the option of MRI (magnetic resonance imaging) screenings in addition to mammograms and encouraging consideration of anti-estrogen therapies that could reduce their risk of developing cancer."

Medical News Today recently reported on a study by researchers from the Washington University School of Medicine in St. Louis, MO, which detailed the development of a safe and effective breast cancer vaccine.