Atypical Hyperplasia of the Breast

April 10, 2025

This page was reviewed under our medical and editorial policy by Susan Yost, Ph.D., staff scientist, Department of Medical Oncology & Therapeutics Research, City of Hope^® Cancer Center Duarte

Atypical breast hyperplasia is a condition that causes changes in a person’s breast tissue. While these changes may be seen on a mammogram, hyperplasia is diagnosed by removing a sample of tissue for examination (biopsy).

During the biopsy procedure, a piece of breast tissue is removed using a needle or surgery. This tissue sample is then examined under a microscope by a doctor called a pathologist, who is trained to examine cells and tissues.

If the breast biopsy indicates atypical breast hyperplasia is present, the doctor will explain the diagnosis. The patient may also see it listed on the pathologist’s report.

What Is Atypical Hyperplasia of the Breast?

Breast hyperplasia is a condition found in about 10% of noncancerous breast biopsies, according to researchers in the American Society of Clinical Oncology’s Journal of Clinical Oncology. It is marked by certain changes in the epithelial cells that line the lobules where milk is made and the ducts through which milk flows. These changes include:

• More than the normal number of cells
• More than the usual two layers of cells

If these cells look normal, the condition is called usual hyperplasia, but if they look abnormal or distorted, it is known as atypical hyperplasia.

The overgrowth of cells in atypical hyperplasia rarely causes a lump that may be felt, but the area may be seen on a mammogram.

Men and women may be diagnosed with atypical hyperplasia, although it is rarely found in male breast tissue.

Is Atypical Hyperplasia Breast Cancer?

Atypical hyperplasia is not breast cancer, but the condition may increase a patient’s chances of developing breast cancer in the future.

Breast cancer risk is 4 to 5 times greater for women diagnosed with atypical breast hyperplasia than for those whose tests show no breast tissue abnormalities. However, even though the risk is higher, most women with atypical breast hyperplasia never develop breast cancer.

Types of Atypical Hyperplasia

While there is only one type of usual hyperplasia, there are two types of atypical hyperplasia of the breast:

• Atypical ductal hyperplasia (ADH)
• Atypical lobular hyperplasia (ALH)

For both types, certain changes (mutations) in cellular proteins, DNA and RNA, are thought to be responsible for the unchecked cell growth. These changes may be triggered in part by the hormone estrogen.

Atypical Ductal Hyperplasia

Patients diagnosed with atypical ductal hyperplasia of the breast have an overgrowth of abnormal cells lining the tubes (ducts) that carry milk to the nipple.

ADH has some characteristics in common with ductal carcinoma in situ (DCIS), which is regarded as the earliest stage of breast cancer. Although some cases of atypical ductal hyperplasia may develop into DCIS, it is important to note that ADH is not considered to be cancer, and many women with it will not develop breast cancer.

Atypical Ductal Hyperplasia Treatment

For patients diagnosed with ADH who have had a needle biopsy or incisional biopsy (removal of part of the abnormal tissue), the doctor may recommend an additional biopsy to remove the entire abnormal area. This excisional biopsy helps to rule out the presence of breast cancer cells in the area.

If only ADH cells are found, no other treatment is generally needed.

The doctor may also recommend increased monitoring, such as a yearly mammogram and follow-up breast exams, to watch for signs of breast cancer. Sometimes magnetic resonance imaging (MRI) scans are recommended to check for breast cancer as well. A breast MRI may be particularly important if the patient has other risk factors for the disease.

People diagnosed with ADH may also benefit from certain lifestyle practices to help lower their risk of developing breast cancer, including:

• Limiting or stopping alcohol use
• Maintaining a healthy body weight
• Breastfeeding for several months following childbirth
• Engaging in moderate-intensity activity for about 150 to 300 minutes per week or high-intensity activity for about 75 to 150 minutes per week
• Eating a healthy diet rich in fruits, vegetables and calcium from dairy products
• Using non-hormonal therapy to treat menopause symptoms in place of hormone treatment
• Talking to the doctor about alternatives to oral contraceptives (birth control pills)
• Quitting smoking

In addition, a selective estrogen receptor modulator (SERM) drug called Nolvadex^® (tamoxifen) has been shown to reduce the risk of developing breast cancer in women diagnosed with ADH. This is because many cases of ADH are considered estrogen receptor positive (ER+), which means estrogen may bind to ADH cell receptors to help the cells grow. Tamoxifen works by blocking estrogen from attaching to these receptors to inhibit ADH cell growth. The medicine is only for patients over the age of 35. Patients should discuss all of the risks and benefits of this chemoprevention treatment with their doctor.

Atypical Lobular Hyperplasia

With atypical lobular hyperplasia of the breast, there is an overgrowth of the cells that line the lobules (sacs), which are milk-producing glands at the end of the ducts. These cells are also distorted in appearance.

ALH cells share some features in common with another condition known as lobular carcinoma in situ, or LCIS for short. Both LCIS and ALH are not breast cancer, but having either of these cell changes increases the patient’s risk of developing breast cancer.

Atypical Lobular Hyperplasia Treatment

Treatment for ALH may include excisional biopsy to remove the cell growth and check for cancer cells nearby. Increased screening with breast exams and mammograms is also typically recommended. If only ALH cells are found during excisional biopsy, no further treatment is needed.

Patients over the age of 35 may wish to discuss the benefits and risks of taking a SERM medication like Nolvadex^® (tamoxifen) to lower their risk of breast cancer. This is called chemoprevention.

Patients diagnosed with ALH may also help to lower their chances of developing breast cancer by engaging in preventive lifestyle practices, such as:

• Limiting or stopping alcohol use
• Maintaining a healthy body weight
• Breastfeeding for several months following childbirth
• Engaging in moderate-intensity activity for about 150 to 300 minutes per week or high-intensity activity for about 75 to 150 minutes per week
• Eating a healthy diet rich in fruits, vegetables and calcium from dairy products
• Using non-hormonal therapy to treat menopause symptoms in place of hormone treatment
• Talking to the doctor about alternatives to oral contraceptives (birth control pills)
• Quitting smoking

The dynamic, state-of-the-art breast cancer centers at City of Hope^Ⓡ offer comprehensive, personalized treatment plans combined with a full line of support services for patients and their loved ones. Plus, urgent appointment scheduling is offered to ensure each person is treated as early as possible. The goal is to improve patient outcomes and provide next-level convenience during patients’ day-to-day healing journeys.