Atypical hyperplasia of the breast is a benign (non-cancerous) condition in which the breast tissue has abnormal growth. It is classified as a type of proliferative breast disease, meaning that it is characterized by an increased number of cells in the breast tissue.

Atypical hyperplasia is usually discovered during a routine breast biopsy, and it is considered a risk factor for the development of breast cancer in the future. Women with atypical hyperplasia have an increased risk of developing breast cancer compared to women without this condition, although the absolute risk is still relatively low.

Treatment for atypical hyperplasia typically involves close monitoring and regular follow-up, including regular mammograms and breast exams. In some cases, a woman may be recommended to take preventive measures, such as hormonal therapy or prophylactic (preventive) mastectomy.

If you have been diagnosed with atypical hyperplasia of the breast, it's important to work with a healthcare professional to develop a monitoring and follow-up plan that is tailored to your individual needs and risk factors. It's also important to practice good breast health habits, such as performing self-exams and getting regular mammograms, to help detect any changes or abnormalities as early as possible.

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.

Atypical hyperplasia is generally treated with surgery to remove the abnormal cells and to make sure no in situ or invasive cancer also is present in the area. Doctors often recommend more-intensive screening for breast cancer and medications to reduce your breast cancer risk.

Follow-up tests to monitor for breast cancer

Your doctor may recommend that you undergo tests to screen for breast cancer. This may increase the chance that breast cancer is detected early, when a cure is more likely. Talk about your breast cancer screening options with your doctor. Your options may include:

• Self-exams for breast awareness in order to develop breast familiarity and to detect any unusual breast changes
• Clinical breast exams by your health care provider annually
• Screening mammograms annually
• Additional breast cancer screening tests, such as breast MRI or molecular breast imaging, based on your other risk factors for breast cancer