Atypical hyperplasia is a precancerous condition that affects cells in the breast. Atypical hyperplasia describes an accumulation of abnormal cells in the breast.
Atypical hyperplasia isn't cancer, but it can be a forerunner to the development of breast cancer. Over the course of your lifetime, if the atypical hyperplasia cells keep dividing and become more abnormal, this can transition into noninvasive breast cancer (carcinoma in situ) or invasive breast cancer.
If you've been diagnosed with atypical hyperplasia, you have an increased risk of developing breast cancer in the future. For this reason, doctors often recommend intensive breast cancer screening and medications to reduce breast cancer risk.
Atypical hyperplasia usually doesn't cause any specific symptoms.
When to see a doctor
Make an appointment with your doctor if you have any signs or symptoms that worry you.
Atypical hyperplasia typically doesn't cause symptoms, but it may cause changes to appear on a mammogram. Atypical hyperplasia is usually discovered during a breast biopsy to investigate an abnormality found on a mammogram. Sometimes atypical hyperplasia is discovered on a biopsy done for a different condition.
It's not clear what causes atypical hyperplasia.
Atypical hyperplasia forms when breast cells become abnormal in number, size, shape, growth pattern and appearance. The appearance of the abnormal cells determines the type of atypical hyperplasia:
- Atypical ductal hyperplasia causes abnormal cells that appear similar to the cells of the breast ducts.
- Atypical lobular hyperplasia causes abnormal cells that appear similar to the cells of the breast lobules.
Atypical hyperplasia is thought to be part of the complex transition of cells that may evolve into breast cancer. The progression to breast cancer typically involves:
- Hyperplasia. The process begins when normal cell development and growth become disrupted, causing an overproduction of normal-looking cells (hyperplasia).
- Atypical hyperplasia. The excess cells stack upon one another and begin to take on an abnormal appearance. At this point, the cells have some, but not all, of the changes needed to become cancer.
- Noninvasive (in situ) cancer. The abnormal cells continue to progress in appearance and multiply, evolving into in situ cancer, in which cancer cells remain confined to the area where they start growing.
- Invasive cancer. Left untreated, the cancer cells may eventually become invasive cancer, invading surrounding tissue, blood vessels or lymph channels.
Increased risk of breast cancer
If you've been diagnosed with atypical hyperplasia, you have an increased risk of developing breast cancer in the future.
Women with atypical hyperplasia have a lifetime risk of breast cancer that is about four times higher than that of women who don't have atypical hyperplasia. The risk of breast cancer is the same for women with atypical ductal hyperplasia and women with atypical lobular hyperplasia.
Recent research has revealed that the risk of breast cancer increases in the years after an atypical hyperplasia diagnosis:
- At 5 years after diagnosis, about 7 percent of women with atypical hyperplasia may develop breast cancer. Put another way, for every 100 women diagnosed with atypical hyperplasia, 7 can be expected to develop breast cancer five years after diagnosis. And 93 will not be diagnosed with breast cancer.
- At 10 years after diagnosis, about 13 percent of women with atypical hyperplasia may develop breast cancer. That means for every 100 women diagnosed with atypical hyperplasia, 13 can be expetected to develop breast cancer 10 years after diagnosis. And 87 will not develop breast cancer.
- At 25 years after diagnosis, about 30 percent of women with atypical hyperplasia may develop breast cancer. Put another way, for every 100 women diagnosed with atypical hyperplasia, 30 can be expected to develop breast cancer 25 years after diagnosis. And 70 will not develop breast cancer.
Being diagnosed with atypical hyperplasia at a younger age may increase the risk of breast cancer even more. For example, women diagnosed with atypical hyperplasia before age 45 seem to have a greater risk of developing breast cancer during their lifetimes.
Discuss your risk of breast cancer with your doctor. Understanding your risk can help you make decisions about breast cancer screening and risk-reducing medications.