Flat epithelial atypia (FEA) of the breast

by Jason Wasserman MD PhD FRCPC
August 10, 2025

Flat epithelial atypia (FEA) is a non-cancerous change that occurs in the small glands of the breast called terminal duct lobular units (TDLUs). In FEA, the normal cells lining the glands are replaced by one or more layers of mildly abnormal cells. These abnormal cells are usually cuboidal or column-shaped and look similar to the cells found in certain early-stage breast cancers, but FEA itself is not cancer.

FEA is part of a group of breast changes called columnar cell lesions, which also includes columnar cell change and columnar cell hyperplasia. Among these, FEA is the only one with atypia — a term pathologists use to describe cells that look different from normal under the microscope.

Where in the breast is flat epithelial atypia found?

Like other columnar cell lesions, FEA occurs in the terminal duct lobular units — the small lobules and ducts that produce and carry milk. These changes are microscopic and cannot be felt during a breast exam.

What causes flat epithelial atypia?

The exact cause is not fully understood. However, research has shown that FEA shares many biological and molecular features with other low-grade breast lesions such as atypical ductal hyperplasia (ADH), low-grade ductal carcinoma in situ (DCIS), and some low-grade invasive cancers (for example, tubular carcinoma).

These similarities include specific genetic changes, such as the loss of part of chromosome 16 (called 16q loss). Because of these shared features, FEA is thought to be an early step in the “low-grade breast neoplasia pathway.” This is a series of changes in breast tissue that can, in some cases, lead to certain low-grade breast cancers.

How is flat epithelial atypia found?

FEA usually does not cause any symptoms. Most cases are found during a screening mammogram. It is often associated with microcalcifications — tiny deposits of calcium that show up as small white spots on a mammogram. Less often, FEA is found by chance when a biopsy is done for another reason.

How is this diagnosis made?

FEA is diagnosed by looking at a breast tissue sample under a microscope. The sample is most often collected with a core needle biopsy, usually after a mammogram shows microcalcifications. The pathologist makes the diagnosis based on the characteristic flat growth pattern and the mild but distinct changes in how the cells look.

What does flat epithelial atypia look like under the microscope?

When examined under the microscope, the glands in the affected lobules are enlarged and lined by one to several layers of uniform, mildly atypical cells. These cells often have small, round nuclei with evenly distributed chromatin (the DNA inside the nucleus) and inconspicuous nucleoli.

The cells may have small projections called apical snouts, and the glands often contain secretions or microcalcifications. The overall growth pattern is flat — there are no complex structures such as bridges, arcs, or micropapillae, which helps distinguish FEA from more advanced lesions like low-grade DCIS.

Is flat epithelial atypia a type of cancer?

No. FEA is not cancer. However, it can sometimes be found alongside other higher-risk lesions, and in rare cases it may be a very early step toward certain low-grade breast cancers. Most people with FEA will never develop cancer as a result of this finding.

Does flat epithelial atypia increase my risk of breast cancer?

FEA may be linked to a small increase in the risk of developing breast cancer in the future. This risk is much lower than that associated with atypical ductal hyperplasia (ADH) or atypical lobular hyperplasia (ALH). The risk also depends on whether other higher-risk changes are present in the same biopsy.

What happens after a diagnosis of flat epithelial atypia?

The next steps depend on your imaging findings, whether the biopsy removed all of the area seen on the mammogram, and whether other higher-risk lesions were found. In some cases, no further surgery is needed. In others, your doctor may recommend removing more tissue to make sure there are no more advanced changes nearby. Radiology–pathology correlation — comparing your mammogram and biopsy results — is important to decide on follow-up.

Prognosis

The outlook for women with FEA is excellent. Most women do not develop further problems from this finding. Your healthcare team will use your overall risk factors to decide on the right schedule for future breast screening.

Questions to ask your doctor

  • Was flat epithelial atypia the only finding in my biopsy, or were other changes also present?

  • Did the biopsy remove all of the area that showed on my mammogram?

  • Do I need any further surgery or follow-up imaging?

  • How often should I have mammograms after this finding?

  • How does this result change my overall breast cancer risk?

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