This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'Pleomorphic adenoma is usually arisen from \nSelect and explain. \nA. Minor salivary gland, B. Superficial lobe, C. Parotid gland, D. Sub mandibular gland', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Pleomorphic adenomas present as painless, slow-growing,\xa0mobile discrete masses. They represent about 60% of tumors\xa0in the parotid, are less common in the submandibular glands,\xa0and are relatively rare in the minor salivary glands. \nPleomorphic\xa0adenomas are benign tumors that consist of a\xa0mixture of ductal (epithelial) and myoepithelial cells, so\xa0they exhibit both epithelial and mesenchymal differentiation.\nEpithelial elements are dispersed throughout the\xa0matrix, which may contain variable mixtures of myxoid,\xa0hyaline, chondroid (cartilaginous), and even osseous tissue.\xa0In some pleomorphic adenomas, the epithelial elements\npredominate; in others, they are present only in widely\xa0dispersed foci. This histologic diversity has given rise to\xa0the alternative, albeit less preferred name mixed tumor. \nThe\xa0tumors consistently overexpress the transcription factor\nPLAG1, often because of chromosomal rearrangements\xa0involving the PLAG1 gene, but how PLAG1 contributes to\ntumor development is unknown.\nPleomorphic adenomas typically manifest as rounded, well-demarcated\xa0masses rarely exceeding 6 cm in the greatest\xa0dimension. Although they are encapsulated, in some locations\xa0(particularly the palate), the capsule is not fully developed,\xa0and expansile growth produces protrusions into the\xa0surrounding tissues. The cut surface is grey-white and typically\xa0contains myxoid and blue translucent chondroid\xa0(cartilage-like) areas. The most striking histologic\xa0feature is their characteristic heterogeneity. Epithelial elements resembling ductal or myoepithelial cells are arranged\xa0in ducts, acini, irregular tubules, strands, or even\xa0sheets. These typically are dispersed within a mesenchyme-like\xa0background of loose myxoid tissue containing\xa0islands of chondroid and, rarely, foci of bone (Fig. 14–6).\nSometimes the epithelial cells form well-developed ducts\xa0lined by cuboidal to columnar cells with an underlying layer\xa0of deeply chromatic, small myoepithelial cells. In other\xa0instances, there may be strands or sheets of myoepithelial\xa0cells. Islands of well-differentiated squamous epithelium also\xa0may be present. In most cases, no epithelial dysplasia or\xa0mitotic activity is evident. No difference in biologic behaviour\xa0has been observed between the tumors composed largely of\xa0epithelial elements and those composed largely of mesenchymal\xa0elements.', 'role': 'assistant'}]