by Jason Wasserman MD PhD FRCPC
October 26, 2022
Acinic cell carcinoma is a type of salivary gland cancer. This tumour is most commonly found in the parotid gland; however, it can be found in any of the major or minor salivary glands that are located throughout the head and neck. A similar tumour can also be found in the breast. The tumour is made up of acinar cells that are normally found in the salivary glands.
At present, doctors do not know what causes acinic cell carcinoma. However, most tumours contain a genetic change that places a part of the SCPP gene cluster close to the NR4A3/NOR-1 gene. What causes this genetic change to occur is still unknown.
Most acinic cell carcinomas are slow growing and painless. Depending on the location of the tumour, the tumour may be seen as a lump under the skin or inside surface of the oral cavity. Tumours that show high grade transformation (see below) tend to grow more quickly and may cause pain as the tumour grows into surrounding nerves.
Most acinic cell carcinomas will not metastasize (spread) to lymph nodes or other parts of the body and are cured by surgery alone. However, about half of all tumours that show high grade transformation (see below) are associated with lymph node or distant metastases.
The diagnosis of acinic cell carcinoma can be made after a small sample of the tumour is removed in either a core needle biopsy or fine needle aspiration biopsy (FNAB). The diagnosis can also be made after the entire is removed in an excision or resection. The tissue removed is then sent to a pathologist for examination under the microscope.
When examined under the microscope, the tumour cells in most acinic cell carcinomas look very similar to the acinar cells normally found in the salivary glands. Like normal acinar cells, the tumour cells contain small round structures called zymogen granules which can be seen on the routine H&E stained slide and when special stains such as PAS and PAS-D are performed. The tumour cells are often arranged in groups called sheets or in round structures called cysts or follicles. In many cases, the tumour cells are surrounded by immune cells called lymphocytes. Pathologists describe this as “tumour-associated lymphoid proliferation” (TALP).
High grade transformation in acinic cell carcinoma means that the tumour has started to change in a way that results in more aggressive behaviour. When examined under the microscope, tumours with high grade transformation have lost some of the features typically seen in an acinic cell carcinoma. In particular, the tumour cells will no longer look like normal acinar 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.
Lymphovascular invasion means that cancer cells were seen inside a blood vessel or lymphatic vessel. Blood vessels are long thin tubes that carry blood around the body. Lymphatic vessels are similar to small blood vessels except that they carry a fluid called lymph instead of blood. The lymphatic vessels connect with small immune organs called lymph nodes that are found throughout the body. Lymphovascular invasion is important because cancer cells can use blood vessels or lymphatic vessels to spread to other parts of the body such as lymph nodes or the lungs. If lymphovascular invasion is seen, it will be included in your report. However, it is rare for lymphovascular invasion to be found in acinic cell carcinoma.
Perineural invasion is a term pathologists use to describe cancer cells attached to or inside a nerve. A similar term, intraneural invasion, is used to describe cancer cells inside a nerve. Nerves are like long wires made up of groups of cells called neurons. Nerves are found all over the body and they are responsible for sending information (such as temperature, pressure, and pain) between your body and your brain. Perineural invasion is important because the cancer cells can use the nerve to spread into surrounding organs and tissues. This increases the risk that the tumour will regrow after surgery. If perineural invasion is seen, it will be included in your report. However, it is rare for perineural invasion to be found in acinic cell carcinoma.
Lymph nodes are small immune organs found throughout the body. Cancer cells can spread from a tumour to lymph nodes through small vessels called lymphatics. The cancer cells in acinic cell carcinoma typically do not spread to lymph nodes and for this reason, lymph nodes are not always removed at the same time as the tumour. However, when lymph nodes are removed, they will be examined under a microscope and the results will be described in your report.
Cancer cells typically spread first to lymph nodes close to the tumour although lymph nodes far away from the tumour can also be involved. For this reason, the first lymph nodes removed are usually close to the tumour. Lymph nodes further away from the tumour are only typically removed if they are enlarged and there is a high clinical suspicion that there may be cancer cells in the lymph node. Most reports will include the total number of lymph nodes examined, where in the body the lymph nodes were found, and the number (if any) that contain cancer cells. If cancer cells were seen in a lymph node, the size of the largest group of cancer cells (often described as “focus” or “deposit”) will also be included.
The examination of lymph nodes is important for two reasons. First, this information is used to determine the pathologic nodal stage (pN). Second, finding cancer cells in a lymph node increases the risk that cancer cells will be found in other parts of the body in the future. As a result, your doctor will use this information when deciding if additional treatment such as chemotherapy, radiation therapy, or immunotherapy is required.
Pathologists often use the term “positive” to describe a lymph node that contains cancer cells. For example, a lymph node that contains cancer cells may be called “positive for malignancy” or “positive for metastatic carcinoma”.
Pathologists often use the term “negative” to describe a lymph node that does not contain any cancer cells. For example, a lymph node that does not contain cancer cells may be called “negative for malignancy” or “negative for metastatic carcinoma”.
All lymph nodes are surrounded by a thin layer of tissue called a capsule. Extranodal extension means that cancer cells within the lymph node have broken through the capsule and have spread into the tissue outside of the lymph node. Extranodal extension is important because it increases the risk that the tumour will regrow in the same location after surgery. For some types of cancer, extranodal extension is also a reason to consider additional treatment such as chemotherapy or radiation therapy.
In pathology, a margin is the edge of a tissue that is cut when removing a tumour from the body. The margins described in a pathology report are very important because they tell you if the entire tumour was removed or if some of the tumour was left behind. The margin status will determine what (if any) additional treatment you may require.
Most pathology reports only describe margins after a surgical procedure called an excision or resection has been performed for the purpose of removing the entire tumour. For this reason, margins are not usually described after a procedure called a biopsy is performed for the purpose of removing only part of the tumour. The number of margins described in a pathology report depends on the types of tissues removed and the location of the tumour. The size of the margin (the amount of normal tissue between the tumour and the cut edge) also depends on the type of tumour being removed and the location of the tumour.
Pathologists carefully examine the margins to look for tumour cells at the cut edge of the tissue. If tumour cells are seen at the cut edge of the tissue, the margin will be described as positive. If no tumour cells are seen at the cut edge of the tissue, a margin will be described as negative. Even if all of the margins are negative, some pathology reports will also provide a measurement of the closest tumour cells to the cut edge of the tissue.
A positive (or very close) margin is important because it means that tumour cells may have been left behind in your body when the tumour was surgically removed. For this reason, patients who have a positive margin may be offered another surgery to remove the rest of the tumour or radiation therapy to the area of the body with the positive margin.