by Jason Wasserman MD PhD FRCPC
August 17, 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.