A new study, published in the American Association for Cancer Research's journal Cancer Prevention Research, challenges the current recommendations for management of a type of breast tissue abnormality.

Atypical lobular hyperplasia (ALH) has not previously been thought to progress directly to breast cancer in the same breast, although it can indicate an equal risk of breast cancer across both breasts.

Instead, it was thought that only another abnormality - atypical ductal hyperplasia (ADH) - could lead directly to cancer in the same breast.

Over a million women in the US have a breast biopsy that returns benign findings every year. Dr. Lynn C. Hartmann, professor of oncology at the Mayo Clinic in Rochester, MN, explains:

"About 10% of these biopsies reveal atypical hyperplasia, a premalignant finding with a proliferation of abnormal cells, which have some but not all the features of a breast cancer."

Due to differences in their microscopic appearance, scientists have previously believed that the two types of atypical hyperplasia - ADH and ADL behave differently.

Dr. Hartmann explains:

"Most have considered ADH a direct precursor to breast cancer, arguing that it requires complete surgical excision while others have maintained that ALH serves as an indicator of heightened and equal risk of breast cancer across both breasts and does not need complete surgical removal."

"Moreover," she says, "some experts have argued that women with atypia develop 'better risk' breast cancers, meaning low-grade cancers with a good prognosis."

What does the new study say?

Over the span of 12.5 years, Dr. Hartmann and her colleagues followed 698 women who had been confirmed - through biopsies - as having these types of breast atypia. Of these patients, 330 had ADH, 327 had ALH and 32 had both.

The researchers found that both types of atypia were equally likely to progress to cancer in the breast. In the study, both ADH and ADL had a 2:1 likelihood of developing into breast cancer.

Both of the types of atypia resulted in invasive ductal cancers in the breast that the abnormality was detected in. About 69% of the atypias that progressed to cancers in these patients were of "intermediate or high grade." About 25% of the cancers had also spread to the lymph nodes.

"If a woman has a breast biopsy and if it shows atypia, it might be wise for her to be seen at a breast center for recommendations about surveillance and preventive therapy options," says Hartmann. "We hope these data will further help clinicians make informed decisions for breast atypia management strategies."

In 2013, a study published in the journal Radiology suggested that patients with confirmed ALH may not always be at risk enough to require surgery.