by Jason Wasserman MD PhD FRCPC
November 16, 2023

An intraductal papilloma is a non-cancerous type of breast tumour. It is called “intraductal” because it is found inside (“intra”) a small open space called a duct. The purpose of a duct is to provide a path for milk to flow from the glands deep inside the breast to the nipple.

About this article

This article was written by doctors to help you read and understand your pathology report for intraductal papilloma of the breast. The sections below describe the results found in most pathology reports, however, all reports are different and results may vary. Contact us if you have any questions about this article or your pathology report. Read this article for a more general introduction to the parts of a typical pathology report.

Where are these tumours normally found?

Intraductal papilloma can be found anywhere in the breast. Tumours in the central (middle) part of the breast just below the nipple tend to be larger while those that develop near the periphery (outside) of the breast are smaller.

What are the symptoms of intraductal papilloma?

Intraductal papillomas that are located in the centre of the breast under the nipple may cause clear or bloody discharge from the nipple. Larger tumours may occasionally feel like a lump under the nipple. Smaller papillomas and those located in the periphery of the breast often do not cause any symptoms and may be found incidentally (by accident) when imaging of the breast is performed for another reason.

What causes an intraductal papilloma?

At present doctors do not know what causes an intraductal papilloma.

What does this tumour look like under the microscope?

When examined under the microscope, an intraductal papilloma is made up of ductal cells that are surrounded by specialized myoepithelial cells. These two cell types connect to form finger-like structures called papillae that are located entirely within spaces called ducts. A test called immunohistochemistry may be performed to confirm the diagnosis. This test makes it easier for pathologists to see both the ductal and myoepithelial cells.

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

A variety of non-cancerous changes can be seen in an intraductal papilloma. The two most common changes are called usual ductal hyperplasia (UDH) and apocrine metaplasia. When these changes are seen they will usually be described in your pathology report.

Can precancerous or cancerous conditions develop in an intraductal papilloma?

Yes, the same precancerous and cancerous conditions that develop in other parts of the breast can develop in an intraductal papilloma. The two most common precancerous conditions found in this tumour are called atypical ductal hyperplasia (ADH) and ductal carcinoma in situ (DCIS). These precancerous conditions are more commonly seen in tumours that develop in the periphery of the breast. A test called immunohistochemistry may be performed to support the diagnosis of ADH or DCIS. Tumours with ADH or DCIS should be removed completely because they are associated with an increased risk of developing a type of breast cancer called invasive ductal carcinoma.

What is a margin and why are margins important?

A margin is the normal tissue that surrounds a tumour and is removed with the tumour at the time of surgery. A margin is considered ‘positive’ when the tumour cells are seen at the cut edge of the tissue. Because intraductal papilloma is a non-cancerous tumour, the report may simply state that the tumour was completely excised, or that margins are negative. Margins are only described in your report after the entire tumour has been removed.

Other helpful resources

Atlas of Pathology