Acinic cell tumors of salivary glands. Frequency and morphological study

Among 873 salivary gland tumors, 15 cases of acinic cell tumors were found (frequency of 1.6%). They occurred approximately evenly in man and women, the mean age being 41 years. They were located principally in the major salivary glands (12 cases in the parotid and 1 case in the submandibular gland) and only twice in accessory glands. Histologically, these tumors were divided into two groups: group I = highly differentiated tumors (less than 20% undifferentiated cells) and group II = poorly differentiated tumors (more than 20% undifferentiated cells). These histological feature seems to play a role in the clinical behaviour of these neoplasms. Thus, the 9 patients with highly differentiated tumors were alive and well 5 to 22 years after the treatment. On the other hand, 5 of the 6 patients with poorly differentiated tumors had local recurrences (4 cases) and lethal metastases to distant lymph nodes and bone (3 cases). The ultrastructural study corroborated the analogy of differentiated tumoral cells with normal acinic cells (numerous secretory granules and ergastoplasmic cisternae). Moreover, the undifferentiated cells had numerous ribosomes and their morphological structure was similar to that of intercalated duct cells. The histogenesis of this rare tumor is discussed. The acinic cell tumor seems more likely to arise from immature cells of intercalated ducts than from adult acinic cells.