Overview

Atypical hyperplasia is a precancerous condition that affects cells in the breast. Atypical hyperplasia describes an accumulation of abnormal cells in the milk ducts and lobules of the breast.

Atypical hyperplasia isn't cancer, but it increases the risk of breast cancer. Over the course of your lifetime, if the atypical hyperplasia cells accumulate in the milk ducts or lobules 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.

Symptoms

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 is typically found during a breast biopsy to investigate an abnormality found on a mammogram or ultrasound. Sometimes atypical hyperplasia is discovered on a biopsy done to investigate a breast concern, such as a lump or nipple discharge.

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Causes

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 describes abnormal cells within the breast ducts.
  • Atypical lobular hyperplasia describes abnormal cells within the breast lobules.

Atypical hyperplasia is thought to be part of the complex transition of cells that may accumulate and 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.
  • 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 milk ducts.
  • Invasive cancer. The abnormal cells accumulate within the duct and continue to multiply and transition to become cancer cells. Invasive cancer tends to invade surrounding tissue, blood vessels or lymph channels.

Complications

If you've been diagnosed with atypical hyperplasia, you have a risk factor that increases your risk of developing breast cancer in the future. The risk of breast cancer in those with atypical hyperplasia is about four times higher than in those who don't have hyperplasia. The risk is similar for atypical ductal hyperplasia and atypical lobular hyperplasia.

Researchers who studied women with atypical hyperplasia found breast cancer risk increased over time:

  • At 5 years after diagnosis, about 7% 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% 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% 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.

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.

Jan. 16, 2021
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