Basal cell adenocarcinoma of the salivary glands

by Jason Wasserman MD PhD FRCPC
June 28, 2024

Basal cell adenocarcinoma is a rare malignant (cancerous) tumour that arises in the salivary glands. It originates from the basal cells, which are cells that line the outer layer of the salivary gland ducts. Most basal cell adenocarcinomas arise in the parotid gland, the largest salivary gland in front of the ear. However, these tumours can also be found in the other major salivary glands, such as the submandibular and sublingual glands, as well as in the minor salivary glands located throughout the oral cavity and throat.

What are the symptoms of basal cell adenocarcinoma?

The symptoms of basal cell adenocarcinoma can vary depending on the location and size of the tumour. Common symptoms include:

• A painless lump or mass in the region of the affected salivary gland (commonly the parotid gland).
• Swelling or enlargement of the affected area.
• Pain or discomfort if the tumour compresses nearby structures or nerves.
• Facial asymmetry due to the growth of the tumour.
• Difficulty swallowing or a sensation of fullness in the throat if the tumour is located in the minor salivary glands within the mouth or throat.
• Numbness or weakness in the face if the facial nerve is involved.

What causes a basal cell adenocarcinoma?

A small number (less than 15% of all tumours) arise in patients with a genetic syndrome called familial/multiple cylindromatosis. However, for most patients with this type of cancer, the cause remains unknown.

How is this diagnosis made?

The diagnosis of basal cell adenocarcinoma is typically only made after the entire tumour has been removed and sent to a pathologist for examination under the microscope.

Microscopic features of this tumour

When examined under the microscope, basal cell adenocarcinoma is predominantly made up of large dark blue cells. These cells are often described as basaloid because they resemble the basal cells normally found in the salivary gland. The cells are typically arranged in large groups, which may be described as sheets or solid growth. The groups may also be surrounded by an eosinophilic (bright pink) material that resembles the basement membrane normally produced by basal cells. Mitotic figures (tumour cells dividing to create cells) are usually found throughout the tumour.

What other tests may be performed to confirm the diagnosis?

Other tests, including immunohistochemistry (IHC) and next-generation sequencing (NGS), may be performed to confirm the diagnosis and rule out other conditions that can look very similar to basal cell adenocarcinoma under the microscope. When immunohistochemistry is performed, the tumour cells are typically positive for cytokeratin 5, p40, S100, and SOX-10.

High grade transformation

High grade transformation in basal cell adenocarcinoma means that the tumour has started to change, resulting in more aggressive behaviour. When examined under the microscope, tumours with high grade transformations have lost some of the features typically seen in a basal cell adenocarcinoma. In particular, the tumour cells will no longer look like normal basal cells. These cells may be described as being atypical or pleomorphic. In addition, tumours with high grade transformation often have more mitotic figures (tumour cells dividing to create new tumour cells), and a type of cell death called necrosis may also be seen. High grade transformation is important because these tumours are more likely to metastasize (spread) to lymph nodes and the lungs.

Perineural invasion

Perineural invasion (PNI) is the process by which cancer cells spread along or around nerves. This phenomenon is significant in head and neck cancers, including basal cell adenocarcinoma. Cancer cells can travel along the nerve fibres to reach areas beyond the primary tumour site when they invade the perineural spaces. Perineural invasion is an important pathological feature because it can indicate a higher risk of local recurrence and can be associated with a more aggressive disease course. Symptoms related to perineural invasion may include pain or nerve dysfunction, depending on the nerves involved.

Lymphovascular invasion

Lymphovascular invasion (LVI) refers to the presence of cancer cells within the lymphatic system or blood vessels. This type of invasion is a critical step in the metastatic spread of cancer, as it allows tumour cells to travel through the lymphatic system or bloodstream to distant sites in the body. In basal cell adenocarcinoma, lymphovascular invasion is important in determining the prognosis and guiding treatment decisions. The presence of lymphovascular invasion typically suggests a higher likelihood of metastasis, particularly to regional lymph nodes or other organs, which can affect the overall treatment approach and outcome.

Margins

In pathology, a margin is the edge of tissue removed during tumour surgery. The margin status in a pathology report is important as it indicates whether the entire tumour was removed or if some was left behind. This information helps determine the need for further treatment.

Pathologists typically assess margins following a surgical procedure, like an excision or resection, that removes the entire tumour. Margins aren’t usually evaluated after a biopsy, which removes only part of the tumour. The number of margins reported and their size—how much normal tissue is between the tumour and the cut edge—vary based on the tissue type and tumour location.

Pathologists examine margins to check if tumour cells are present at the tissue’s cut edge. A positive margin, where tumour cells are found, suggests that some cancer may remain in the body. In contrast, a negative margin, with no tumour cells at the edge, suggests the tumour was fully removed. Some reports also measure the distance between the nearest tumour cells and the margin, even if all margins are negative.

Lymph nodes​

Small immune organs, known as lymph nodes, are located throughout the body. Cancer cells can travel from a tumour to these lymph nodes via tiny lymphatic vessels. For this reason, doctors often remove and microscopically examine lymph nodes to look for cancer cells. This process, where cancer cells move from the original tumour to another body part, like a lymph node, is termed metastasis.

Cancer cells usually first migrate to lymph nodes near the tumour, although distant lymph nodes may also be affected. Consequently, surgeons typically remove lymph nodes closest to the tumour first. They might remove lymph nodes farther from the tumour if they are enlarged and there’s a strong suspicion they contain cancer cells.

Pathologists will examine any removed lymph nodes under a microscope; the findings will be detailed in your report. A “positive” result indicates the presence of cancer cells in the lymph node, while a “negative” result means no cancer cells were found. If the report finds cancer cells in a lymph node, it might also specify the size of the largest cluster of these cells, often referred to as a “focus” or “deposit.” Extranodal extension occurs when tumour cells penetrate the lymph node’s outer capsule and spread into the adjacent tissue.

Examining lymph nodes is important for two reasons. First, it helps determine the pathologic nodal stage (pN). Second, discovering cancer cells in a lymph node suggests an increased risk of later finding cancer cells in other body parts. This information guides your doctor in deciding whether you need additional treatments, such as chemotherapy, radiation therapy, or immunotherapy.

About this article

Doctors wrote this article to help you read and understand your pathology report for basal cell adenocarcinoma. The sections above describe the results found in most pathology reports. However, all reports are different, and results may vary. Importantly, some of this information will only be described in your report after the entire tumour has been surgically removed and examined by a pathologist. Contact us if you have any questions about this article or your pathology report.

Other helpful resources

Atlas of Pathology