By Jason Wasserman MD PhD FRCPC
March 20, 2023
A biphasic salivary gland neoplasm is a tumour that arises in one of the salivary glands. It is called biphasic because it is made up of two distinct populations of cells: luminal cells (ductal cells) and abluminal cells (basal cells or myoepithelial cells). The luminal cells are typically large round or cuboidal-shaped cells that connect to form round structures called ducts or glands. The abluminal cells are smaller and they are often found on the outside or periphery of the ducts and glands. Myoepithelial-type abluminal cells are often described as spindle cells because they are long and thin. There are several different kinds of salivary gland tumours that can be described as biphasic salivary gland neoplasm.
The diagnosis of biphasic salivary gland neoplasm is typically used after a biopsy has been performed and a small sample of the tumour has been examined under the microscope by a pathologist. The small sample allows the pathologist to determine that the tumour is biphasic, which means it is made up of two types of cells (luminal and abluminal) but a more definitive or final diagnosis cannot be reached. In this situation, a definitive or final diagnosis will be provided after the entire tumour is removed and examined. In some situations, the term biphasic salivary gland neoplasm may also be used even after the entire tumour has been removed but while the pathologist is waiting for additional tests (for example next-generation sequencing) to help confirm the diagnosis.
Pathologists use the term favoured when multiple diagnoses are being considered but there is one diagnosis, they think is most likely. For example, the diagnosis “biphasic salivary gland neoplasm, favour pleomorphic adenoma” means that the microscopic features were in keeping with a biphasic salivary gland neoplasm (a group which includes many types of tumours) but that the pathologist thinks pleomorphic adenoma (a specific type of salivary gland tumour) is the most likely diagnosis.
The most common type of biphasic salivary gland neoplasm is pleomorphic adenoma. Pleomorphic adenoma can arise in any of the salivary glands although it is most commonly found in the parotid gland.
The most common type of malignant biphasic salivary gland neoplasm is adenoid cystic carcinoma.