Large cell undifferentiated carcinoma is a malignant neoplasm that lacks any features of differentiation. However, in some instances poorly formed duct-like structures have been described. Rapid growth of a parotid swelling is a common clinical presentation (Gaughan, Olsen, and Lewis 1992). These tumors are high-grade lesions that commonly metastasize. Tumors that are T3 or greater have been noted to have a dire prognosis (Batsakis and Luna 1991). These neoplasms make up only -1% of all epithelial salivary gland tumors, with the vast majority of cases occurring in the parotid glands of elderly patients (Batsakis and Luna 1991; Ellis and Auclair 1996; Hui et al. 1990).
Lymphoepithelial Carcinoma Lymphoepithelial carcinoma, which is also known as undifferentiated carcinoma with lymphoid stroma and carcinoma ex-lymphoepithelial lesion, is an undifferentiated tumor coupled with a dense lymphoid stroma; notably these lesions have been linked with Epstein-Barr virus infection (Leung et al. 1995). Moreover, an unusually high incidence of these tumors has been identified most often in the parotid glands and to a lesser extent in the submandibular gland of Eskimo and Inuit populations (Bosch, Kudryk, and Johnson 1988; Ellis and Auclair 1996). Pain is a common presenting symptom; however, in 20% of patients facial nerve involvement has been recorded (Borg et al. 1993). Cervical lymph node metastasis has been a common finding at initial presentation, and 20% of patients develop distant metastases within a 3-year period (Borg et al. 1993; Bosch, Kudryk, and Johnson 1988).
Myoepithelial Carcinoma Myoepithelial carcinoma is a very rare, malignant salivary gland neoplasm that almost entirely manifests myoepithelial differentiation. This tumor represents the malignant complement of benign myoepithelioma (Ellis and Auclair 1996). The majority of patients, mean age 55 years, present with a painless mass generally within the parotid gland (66%) (Ellis and Auclair 1996). The tumors are often intermediate-grade or high-grade carcinomas (Ellis and Auclair 1996; Savera et al. 2000). Interestingly, the histological grade of these neoplasms does not appear to correlate in a good way with clinical behavior, in that some tumors manifesting with a low-grade histologic pattern may behave in an aggressive manner (Savera et al. 2000).
Adenosquamous Carcinoma Adenosquamous carcinoma is an extremely uncommon malignant neoplasm that emerges concurrently from surface mucosa and salivary gland ductal epithelium. These tumors possess histo-pathological characteristics of squamous cell carcinoma and of adenocarcinoma. Analysis of the few cases reported seems to indicate that this is an extremely aggressive malignancy with a dismal prognosis (Ellis and Auclair 1996).
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