Your pathology report for intraductal carcinoma of the salivary glands

by Jason Wasserman MD PhD FRCPC
August 7, 2025

Intraductal carcinoma (IDC) is a rare type of noninvasive cancer that starts in the salivary glands, most often in the parotid gland. In this condition, the abnormal cells grow inside the small ducts of the gland and remain surrounded by a protective layer of myoepithelial cells. Because the tumor stays confined to the ducts, IDC is considered an in situ cancer, meaning it has not spread into nearby tissue.

IDC is usually slow-growing and does not spread to lymph nodes or other parts of the body. Most tumors are cured with surgery alone, and no additional treatment is needed. However, in rare cases, the tumor may show invasive growth, meaning it has spread beyond the ducts into surrounding tissue. These invasive cases, called carcinoma ex intraductal carcinoma, behave more aggressively and often require further treatment.

What are the symptoms of intraductal carcinoma?

Many patients with IDC do not experience any symptoms in the early stages. The most common sign is a painless swelling in the region of a salivary gland, most often near the ear or under the jaw. The swelling is usually firm and slow-growing. Because IDC tends to grow slowly, many tumors are discovered during imaging or evaluation for unrelated reasons. Pain or rapid growth is uncommon but may occur if the tumor becomes invasive.

Types of intraductal carcinoma

IDC is not a single disease but includes different subtypes, each with its own appearance under the microscope, genetic features, and behavior. A pathologist determines the subtype by examining tissue from the tumor and, in some cases, performing molecular tests.

Intercalated duct type

This is the most common subtype. The tumor cells are small and resemble the normal cells that line intercalated ducts in salivary glands. These tumors typically grow slowly and are considered low-grade, meaning they have a very low risk of spreading or behaving aggressively. Most cases arise in the parotid gland.

Apocrine type

In this subtype, the tumor cells are larger and have a characteristic bubbly, pink appearance. They may produce secretions that resemble those seen in apocrine glands, such as sweat glands. Some apocrine IDCs show signs of more aggressive behavior and are considered higher grade. These tumors are less common than the intercalated type.

Oncocytic type

This rare subtype is made up of oncocytic cells, which are large cells with abundant pink granular cytoplasm. Oncocytic IDC is usually low-grade and behaves in a non-aggressive way. It can occur in the parotid or other salivary glands.

Mixed type

Mixed IDCs show a combination of features from more than one subtype, most often intercalated and apocrine types. The behavior of mixed tumors depends on which component is more dominant. Most mixed IDCs are low-grade, but those with a larger apocrine component may behave more aggressively.

What causes intraductal carcinoma?

The exact cause of IDC is not known, but many tumors show specific genetic changes that help drive the growth of tumor cells. These genetic changes are not inherited but occur spontaneously in the tumor cells. The type of genetic change often depends on the subtype of IDC.

Intercalated duct type

This type is often associated with a gene fusion called NCOA4-RET, where parts of two different genes combine to form a new abnormal gene. This fusion leads to continuous signals that cause cells to grow and divide. Less commonly, other fusions like STRN-ALK or TUT1-ETV5 may be present.

Apocrine type

Apocrine IDC does not usually have gene fusions. Instead, it often shows mutations in genes such as HRAS, PIK3CA, or TP53. These mutations can alter how cells grow and avoid normal controls that prevent cancer.

Oncocytic type

This subtype may show BRAF mutations, most notably the BRAF V600E mutation, or rare gene fusions such as TRIM33-RET or NCOA4-RET.

Mixed type

Mixed intercalated and apocrine IDC frequently shows a TRIM27-RET fusion. This fusion can affect both types of tumor cells.

How is this diagnosis made?

The diagnosis of IDC is made by examining tissue from the salivary gland under a microscope. The tissue is usually obtained through a core needle biopsy or surgical excision. In some cases, fine needle aspiration (FNA) may be used, but a larger tissue sample is usually needed to accurately identify the tumor and determine the subtype.

The pathologist looks for specific features such as the growth pattern, appearance of the tumor cells, and presence of a surrounding layer of myoepithelial cells. Special stains and molecular tests may be performed to confirm the diagnosis and identify any genetic changes.

What does IDC look like under the microscope?

Under the microscope, IDC appears as well-defined rounded or lobulated structures that may be cystic (fluid-filled) or solid. The tumor cells form patterns that may include cribriform (sieve-like), papillary (finger-like), or solid arrangements. The key diagnostic feature is that the tumor cells are confined within a pre-existing duct structure and are surrounded by a continuous layer of myoepithelial cells, which helps distinguish IDC from invasive cancers.

The appearance of the tumor cells varies depending on the subtype:

• Intercalated duct type: Small oval cells with pink to purple cytoplasm.
• Apocrine type: Large cells with bubbly pink cytoplasm and visible secretions.
• Oncocytic type: Large cells with dense, granular, bright pink cytoplasm.
• Mixed type: A combination of the above features.

What other tests may be performed to confirm the diagnosis?

To confirm the diagnosis and help determine the subtype, pathologists may perform several additional tests including immunohistochemistry, in situ hybridization, and next generation sequencing.

Immunohistochemistry (IHC)

This test uses special stains to detect specific proteins in the tumor cells. The pattern of staining helps distinguish between the different subtypes:

• Intercalated duct and oncocytic types usually test positive for proteins such as S100, SOX10, and mammaglobin.
• Apocrine type is usually positive for androgen receptor (AR) and GCDFP-15, and negative for the markers listed above.
• The myoepithelial cells surrounding the tumor test positive for markers such as p40, p63, SMA, and CK14.

In situ hybridization (ISH)

This test looks for specific gene fusions or viruses in the tumor cells. In some cases, ISH may be used to detect RET gene fusions that are present in many intercalated duct and mixed IDCs.

Next generation sequencing (NGS)

This test looks at the DNA or RNA of the tumor to identify mutations or gene fusions. NGS can detect:

• NCOA4-RET or TRIM27-RET fusions in intercalated or mixed types.
• BRAF V600E mutations in oncocytic IDC.
• HRAS and PIK3CA mutations in apocrine IDC.

These results help confirm the diagnosis, especially when the microscopic features are not typical.

What does invasion mean and why is it important?

Intraductal carcinoma with invasion means that cancer cells have spread beyond the ducts and have entered the surrounding normal tissue of the salivary gland or nearby structures. This is an important change because it signals that the tumor is no longer confined to its original space.

In a typical IDC, the cancer cells are completely surrounded by myoepithelial cells, which act as a barrier and prevent the tumor from spreading. When invasion occurs, these myoepithelial cells are lost or disrupted, and the cancer is able to grow into surrounding tissue. This can include nearby nerves, fat, or even blood vessels.

Invasion is important because it changes how doctors classify the tumor and may affect the treatment plan. Tumors that show invasive growth have a higher risk of:

• Spreading to lymph nodes.
• Returning after surgery.
• Needing additional treatment such as radiation therapy or closer follow-up.

If your pathology report shows no invasion, the tumor is considered non-invasive and has a very low risk of recurrence or spread. If invasion is found, your doctor may recommend additional steps to ensure the cancer is fully treated.

Margins

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

• A negative margin means no cancer cells were seen at the edge, suggesting the tumour was completely removed.
• A positive margin means cancer cells are present at the edge, which raises concern that some tumour may have been left behind.

Your report may also describe the distance between the tumour and the nearest margin, especially if all margins are negative. This information helps your doctors decide whether additional surgery or radiation therapy may be needed.

Margins are only evaluated after the entire tumour has been removed in a procedure such as an excision or resection. They are not typically assessed after a biopsy.

What stage is intraductal carcinoma?

Intraductal carcinoma (IDC) is considered a noninvasive cancer, which means it has not spread beyond the salivary gland ducts where it started. Because it is noninvasive, IDC is generally not given a stage using the traditional cancer staging systems that are applied to invasive cancers. In the current Union for International Cancer Control (UICC) and American Joint Committee on Cancer (AJCC) staging guidelines, noninvasive cancers like IDC are sometimes described as in situ disease, which can be thought of as “stage 0.”

This stage reflects that the abnormal cells are still contained within their original location and have not invaded the surrounding tissue or spread to other parts of the body. IDC in this stage is almost always cured with surgery alone.

If an IDC develops an invasive component—meaning the cancer cells have grown beyond the ducts and into nearby salivary gland tissue—it is no longer classified as in situ. Instead, it is staged the same way as other invasive salivary gland cancers, with the stage based on the size of the invasive tumor, whether cancer cells are found in nearby lymph nodes, and whether there is spread to other parts of the body.

Questions to ask your doctor

• What type of intraductal carcinoma do I have?
• Was there any evidence of invasion outside the ducts?
• Do I need any additional treatment after surgery?
• What follow-up plan do you recommend?