by Jason Wasserman MD PhD FRCPC
November 4, 2024
Basal cell adenocarcinoma is a rare type of salivary gland cancer. Compared to other types of salivary gland cancer, it is slow-growing and has less chance of spreading to lymph nodes or other body parts. However, it can still grow and invade nearby tissues, so early diagnosis and treatment are important. 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.
Symptoms of basal cell adenocarcinoma can include a painless lump or swelling in the salivary glands, usually near the jaw or under the chin. If the tumour presses on nearby nerves or tissues, some people may experience discomfort, numbness, or slight pain.
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.
To diagnose basal cell adenocarcinoma, your doctor will typically start with an imaging test, such as an ultrasound, CT scan, or MRI, to assess the size and location of the tumour. If a suspicious area is found, a biopsy will be performed to take a small tissue sample. A pathologist will then examine this sample under a microscope to confirm the diagnosis. Sometimes, additional tests are done to help confirm that the tumour is basal cell adenocarcinoma and to rule out other types of salivary gland cancers.
When a pathologist examines basal cell adenocarcinoma under a microscope, they look for specific patterns in the tumour’s structure. Basal cell adenocarcinomas often show a combination of tubulotrabecular (tube-like) and solid growth patterns, with the solid pattern being the most common. The tumour forms clusters, or nests, of cells with dark cells arranged in a palisading pattern—meaning they line up in rows at the edge of each nest. Inside these nests are lighter-coloured cells and small ducts (tube-like structures).
Sometimes, the tumour may also contain squamous (flat) cells or sebaceous (oil-producing) cells. The nuclei, or control centres of the cells, have a clear and open appearance, referred to as vesicular nuclei.
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 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 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 (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 (LVI) refers to cancer cells within the lymphatic system or blood vessels. This 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. Lymphovascular invasion suggests a higher likelihood of metastasis, particularly to regional lymph nodes or other organs, affecting the overall treatment approach and outcome.
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.
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 lymph nodes removed 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.
Pathologic staging is a system doctors use to describe the size and spread of a tumour. This helps determine how advanced the cancer is and guides treatment decisions. The pathologic stage is usually determined after the tumour is removed and examined by a pathologist, who analyzes the tissue under a microscope. For basal cell adenocarcinoma, staging is based on the “TNM” system, where “T” stands for the size and extent of the primary tumour, “N” refers to lymph node involvement, and “M” indicates whether the cancer has spread to other parts of the body.
The tumour stage describes the size of the tumour in the salivary gland and whether it has spread into nearby tissues.
The nodal stage indicates whether the cancer has spread to the lymph nodes, which are small glands that help the body fight infection. Lymph node involvement can increase the risk of cancer spreading further.
Several pathologic features of basal cell adenocarcinoma can help determine its prognosis or the likely outcome. These include the tumour’s size, growth pattern, and whether it has spread to surrounding tissues or lymph nodes. Tumours that are smaller and confined to the salivary gland tend to have a better prognosis. If the tumour has grown into nearby tissues or lymph nodes, it may be more challenging to treat and may require a combination of surgery and other therapies.
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 with any questions about this article or your pathology report.