Your pathology report for intraductal papilloma of the breast

by Jason Wasserman MD PhD FRCPC
October 6, 2025

An intraductal papilloma is a non-cancerous (benign) tumor that develops inside one of the small milk ducts in the breast. The word intraductal means “inside the duct,” and the word papilloma refers to the small finger-like projections (called papillae) that form within the duct.

Milk ducts are tiny channels that carry milk from the glands deep in the breast to the nipple. Intraductal papillomas can develop in any of these ducts and are among the most common benign breast tumors diagnosed by pathologists.

Where are these tumors commonly found?

Intraductal papillomas can occur anywhere in the breast.

• Tumors located in the central part of the breast, just beneath the nipple, tend to be larger and are sometimes called solitary papillomas.

• Tumors that form near the outer (peripheral) parts of the breast are usually smaller and may be multiple.

Peripheral papillomas are often found during imaging studies or biopsies performed for another reason.

What are the symptoms of intraductal papilloma?

In many cases, intraductal papillomas do not cause any symptoms and are discovered incidentally on a mammogram or ultrasound.

When symptoms occur, they can include:

• Nipple discharge, which may be clear or bloody, is especially common when the papilloma is located under or behind the nipple.

• A small lump or thickened area beneath the nipple.

• Tenderness or discomfort in the area (less common).

Papillomas located deeper in the breast (peripheral papillomas) rarely cause discharge and are usually too small to feel.

What causes an intraductal papilloma?

The exact cause of intraductal papilloma is not known. Most cases are sporadic, meaning they occur by chance and are not inherited. Hormonal influences, particularly from estrogen, may play a role in the development of these benign tumors, as they appear more commonly in women between the ages of 35 and 55.

How is this diagnosis made?

A pathologist makes the diagnosis of intraductal papilloma after examining breast tissue under the microscope. The tissue is usually obtained from a core needle biopsy or after surgical removal of a small lump or abnormal area seen on imaging.

A test called immunohistochemistry may be performed to confirm the diagnosis. This special test utilizes antibodies that highlight different cell types, enabling the pathologist to identify both the ductal epithelial cells (the cells lining the ducts) and the myoepithelial cells (specialized cells that form a supporting layer around the ducts and help squeeze milk toward the nipple).

What does this tumor look like under the microscope?

Under the microscope, an intraductal papilloma is made up of finger-like papillary structures that project into a duct.

Two types of cells line these papillae:

• Ductal epithelial cells, which form the inner lining of the duct.

• Myoepithelial cells, which form an outer layer and help confirm that the lesion is benign.

Together, these cells form branching structures supported by thin cores of connective tissue and small blood vessels. The presence of a continuous layer of myoepithelial cells is one of the key features that distinguishes a benign papilloma from a papillary carcinoma (a cancerous tumor).

What other non-cancerous changes can be seen in an intraductal papilloma?

Several non-cancerous (benign) changes can occur within an intraductal papilloma. These changes are often described in the pathology report and do not increase the risk of cancer. The most common include:

• Usual ductal hyperplasia (UDH): An increase in the number of normal ductal cells, which may look crowded but are not abnormal.

• Apocrine metaplasia: A non-cancerous change in which ductal cells transform into apocrine cells, which are larger with a pink-colored cytoplasm (the body of the cell) and a round nucleus (the central part of the cell containing DNA).

These findings are common and part of the normal spectrum of fibrocystic changes seen in the breast.

Can precancerous or cancerous conditions develop in an intraductal papilloma?

Yes, in some cases, precancerous or cancerous changes can develop within an intraductal papilloma. The two most common precancerous conditions are:

• Atypical ductal hyperplasia (ADH).

• Ductal carcinoma in situ (DCIS).

These conditions are more often found in peripheral papillomas than in those located under the nipple. When ADH or DCIS is present, it means that some of the ductal cells have begun to grow abnormally, although they have not yet invaded surrounding tissue.

Immunohistochemistry is often used to help confirm these diagnoses. Because ADH and DCIS are associated with an increased risk of developing invasive ductal carcinoma, papillomas showing these changes are usually completely removed by surgery.

What is a margin, and why are margins important?

A margin is the rim of normal tissue surrounding a tumor that is removed during surgery. The pathologist examines these margins to make sure the entire tumor has been taken out.

• A negative (clear) margin means there are no papilloma cells at the edge of the tissue, suggesting complete removal.

• A positive margin means papilloma cells are seen at the cut edge, and additional tissue may need to be removed.

Because intraductal papilloma is a benign tumor, your report may state that the papilloma was completely excised or that margins are negative. Margins are only described when the entire lesion has been removed, not in biopsy samples.

What is the prognosis for intraductal papilloma?

The prognosis for intraductal papilloma is excellent. Once completely removed, recurrence is uncommon, and the vast majority of cases never progress to cancer. Suppose your pathology report mentions atypical ductal hyperplasia (ADH) or ductal carcinoma in situ (DCIS). In that case, your doctor may recommend closer follow-up or additional treatment, as these conditions slightly increase the risk of developing breast cancer in the future.

Questions to ask your doctor

• Was my intraductal papilloma completely removed?

• Did my pathology report mention atypical ductal hyperplasia (ADH) or ductal carcinoma in situ (DCIS)?

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

• What symptoms should I watch for in the future?

• How often should I have breast screening after this diagnosis?