Overall, diseases of the salivary glands are relatively uncommon; however, as an organ system they have one of the greatest diversities of pathology. The vast majority of lesions are of an inflammatory origin; however, some arise from posttraumatic, systemic, or an uncertain pathogenesis. There also is a wide spectrum of benign and malignant neoplasms.<sup>74 Peel R.Z., Gnepp D.R. Diseases of the salivary glands  New York: Marcel Dekker (1985).  535-552

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As a group, the salivary neoplasms account for less than 3% of all head and neck tumors and they account for less than 0.1% of all cancer deaths.<sup>14 Boring C.C., Squires T.S., Tong T. Cancer statistics 1993 CA Cancer Clin 1993 ;  43 : 18-19

Cliccare qui per andare alla sezione Riferimenti</sup> The relative incidence of salivary gland tumors is estimated to be that for every 100 parotid tumors, there are 10 submandibular tumors, 10 minor salivary tumors, and 1 sublingual tumor.<sup>102 Thackray A.C., Lucas R.B. Tumors of the Major Salivary Glands Atlas of Tumor Pathology Washington, DC: Armed Forces Institute of Pathology (1974).  1-15

Cliccare qui per andare alla sezione Riferimenti</sup> The parotid, submandibular, and sublingual glands are often referred to as the major salivary glands, whereas the minor salivary glands line the oral cavity and upper aerodigestive tracts.

With regards to the pathogenesis of salivary gland neoplasms, it was assumed for decades that there were but two potential stem cells from which the variety of different salivary tumors originated. It was generally thought that because the basal cells of the excretory duct and the intercalated duct cells acted as the reserve cells for the more differentiated cells of the salivary gland unit, all of the epithelial tumors arose from these reserve cells rather than from the acini.<sup>8 Batsakis J.G.   Tumors of the Head and Neck: Clinical and Pathological Considerations Baltimore: Williams & Wilkins (1979). 

Cliccare qui per andare alla sezione Riferimenti</sup> Implicit in this concept was the assumption that the differentiated end cells were incapable of further dividing and therefore were incapable of giving rise to tumors.<sup>8 Batsakis J.G.   Tumors of the Head and Neck: Clinical and Pathological Considerations Baltimore: Williams & Wilkins (1979). 

Cliccare qui per andare alla sezione Riferimenti</sup> Recent evidence has shown, however, that salivary glands proliferate and regenerate after injury and that the proliferating cells are not confined to one cell type.<sup>27 Dardick I., Burford-Mason A.P. Current status of histogenic and morphogenetic concepts of salivary gland tumorigenesis Crit Rev Oral Biol Med 1993 ;  4 : 639-677

Cliccare qui per andare alla sezione Riferimenti</sup> Further, in cell cultures from human salivary glands, all of the differentiated cell types have now been shown to be capable of cycling.<sup>28 Dardick I., Dardick A.M., Mackay A.J. , e al. Pathobiology of salivary glands. IV Histogenetic concepts and cycling cells in human parotid and submandibular glands cultures in floating collagen gels Oral Surg Oral Med Oral Pathol 1993 ;  76 : 307-318  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> Thus, the once simple theory for the pathogenesis of the salivary gland tumors appears to be far more diverse than previously thought.