Your pathology report for encapsulated papillary carcinoma of the breast

by Jason Wasserman MD PhD FRCPC
October 6, 2025

Encapsulated papillary carcinoma is a type of breast cancer that is usually non-invasive. Non-invasive means that the cancer cells are confined to the ducts where they started and have not spread into the surrounding breast tissue. This type of tumor behaves in a similar way to ductal carcinoma in situ (DCIS), another non-invasive form of breast cancer.

Under the microscope, encapsulated papillary carcinoma grows in a finger-like pattern, known as papillae, which project into a small, cyst-like space. The tumor is enclosed by a fibrous capsule, a thin layer of connective tissue that separates it from the nearby normal breast tissue. Because the cancer cells are contained within this capsule, the tumor generally grows slowly and has an excellent prognosis when treated appropriately.

What are the symptoms of encapsulated papillary carcinoma?

Many people with encapsulated papillary carcinoma have no symptoms in the early stages, and the tumor is often found incidentally on a screening mammogram.

When symptoms do occur, they can include:

• A lump in the breast that can be felt or seen on imaging

• Nipple discharge, which may occasionally be bloody

It is important to remember that these symptoms can also occur with non-cancerous (benign) breast conditions.

What causes encapsulated papillary carcinoma?

The exact cause is not known. Like many other cancers, encapsulated papillary carcinoma develops after genetic changes (mutations) occur in breast duct cells. These changes cause the cells to grow and divide in an abnormal manner. Most cases occur sporadically, meaning they are not inherited and are not caused by anything the patient did or did not do.

How is this diagnosis made?

The diagnosis of encapsulated papillary carcinoma is made after a biopsy or surgical excision of the breast tissue. In a biopsy, a small piece of the lump is removed and examined under a microscope by a pathologist.

Under the microscope, the pathologist looks for:

• Papillary (finger-like) structures made up of cancer cells.

• A fibrous capsule around the tumor.

• The absence of invasive growth into surrounding tissue.

Special tests, such as immunohistochemistry, may be used to confirm the diagnosis and to help determine whether the tumor behaves more like ductal carcinoma in situ or an invasive carcinoma.

If the entire tumor is surgically removed, additional details, such as margin status and the presence or absence of invasion, will also be described in the pathology report.

What does encapsulated mean, and why is that important?

The word encapsulated refers to the layer of fibrous tissue that surrounds the tumor. This capsule acts as a barrier, keeping the cancer cells contained within a small area.

As long as the tumor cells remain within this capsule, the cancer is considered non-invasive, which means it cannot spread to other parts of the body. However, if tumor cells break through the capsule, the cancer becomes invasive, which can change the treatment plan and overall outlook.

What are the microscopic features of encapsulated papillary carcinoma?

Under the microscope, encapsulated papillary carcinoma shows:

• Papillary structures with fibrovascular cores (small stalks of tissue containing blood vessels).

• Tumor cells that often have a uniform appearance with round nuclei (the central part of the cell that contains the genetic material or DNA).

• A surrounding fibrous capsule.

• The absence of myoepithelial cells, which are special cells that normally form a thin layer around ducts and help squeeze out secretions in the breast. Their absence supports the diagnosis of a carcinoma rather than a benign (noncancerous) papilloma.

Sometimes, areas of ductal carcinoma in situ (DCIS) can be seen in the surrounding breast tissue.

Nuclear grade

Pathologists assign a nuclear grade to encapsulated papillary carcinoma based on how abnormal the tumor cell nuclei look and how quickly the cells are dividing. Dividing cells are identified under the microscope by structures called mitotic figures, which show cells in the process of splitting into two new cells.

• Low nuclear grade (grade 1): The tumor cells have small, uniform nuclei and very few mitotic figures (dividing cells).

• Intermediate nuclear grade (grade 2): The nuclei are larger and slightly irregular, with occasional mitotic figures.

• High nuclear grade (grade 3): The nuclei look very abnormal, and mitotic figures are easily seen throughout the tumor.

The nuclear grade is important because a high-grade tumor is more likely to develop invasive cancer in the future compared to a low-grade tumor.

What does encapsulated papillary carcinoma with invasion mean?

Encapsulated papillary carcinoma with invasion means that some tumor cells have moved beyond the capsule and into the surrounding breast tissue. Once invasion occurs, the cancer behaves more like invasive ductal carcinoma, which can spread to nearby lymph nodes or, rarely, to distant sites.

When invasion is present, doctors may recommend additional treatments, such as radiation therapy or, in some cases, systemic treatments (for example, hormone therapy, chemotherapy, or targeted therapy), depending on the tumor’s molecular features.

Margins

A margin is the edge of tissue that is removed during surgery. The pathologist examines the margins under the microscope to see if any cancer cells are present at the cut edge.

• A negative (clear) margin means there are no cancer cells at the edge of the tissue, suggesting the tumor was removed entirely.

• A positive margin means that cancer cells are visible at the edge, which increases the risk that some tumor cells remain in the breast.

If the margin is positive, your doctor may recommend another surgery to remove more tissue or may suggest radiation therapy. A wider negative margin generally reduces the risk of the tumor coming back.

What stage is encapsulated papillary carcinoma?

Encapsulated papillary carcinoma without invasion is staged as pTis (carcinoma in situ), which is the same stage given to ductal carcinoma in situ (DCIS). This staging indicates that the tumor is confined to its original site and has not spread into surrounding breast tissue.

When invasion is present, the stage increases to pT1 or higher, depending on the size and extent of the invasive component. Most non-invasive encapsulated papillary carcinomas are considered indolent, meaning they are slow-growing and have an excellent prognosis.

What is the prognosis for encapsulated papillary carcinoma?

The prognosis for encapsulated papillary carcinoma is very good, especially when there is no invasion. Most patients are cured with surgery alone, and the risk of recurrence or spread is extremely low.

If invasion is present or if the tumor has additional high-risk features (such as high nuclear grade, triple-negative, or HER2-positive status), the cancer may behave more like an invasive breast carcinoma, and further treatment may be recommended.

Overall, encapsulated papillary carcinoma is one of the most favorable types of breast cancer to be diagnosed on a pathology report.

Questions to ask your doctor

• Was my tumor non-invasive or invasive?

• What was the nuclear grade of my tumor?

• Were the surgical margins clear?

• Was any ductal carcinoma in situ (DCIS) found nearby?

• Do I need any additional treatment after surgery?

• What is my risk of recurrence?

Other helpful resources

American Breast Cancer Foundation

Canadian Breast Cancer Foundation