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': 'All of the following is involved in tumor metastasis cascade except - \nSelect and explain. \nA. Fibronectin, B. e-cadherin, C. Type IV collagenase, D. Tyrosine kinase', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Invasion and metastasis of tumor \n\nInvasion and metastasis are biological hallmarks of malignant tumors.\nThis involve a series of steps -\n\n\u200bDetachment of tumor cells\n\n\nDetachment of tumor cells is the first step in metastasis.\nNormally cells are glued to each other by adhesion molecules E-cadherin.\nNormal function of E-cadherin is dependent on catenins that helps in linkage of cytoskeleton to E-cadherin.\nDown regulation of expression of either E-cadherins or catenins results loosening of cells that helps in metastasis.\n\n\xa0Attachment to ECM (including basement membrane)\n\nTumor cells express integrins that helps in the attachement of cells to many components of ECM like fibronectin, laminin, vitronectin, and collegen.\n\nDegradation of ECM\n\nAfter attachement to ECM components, tumor cells must create passageways for migration.\nThis require enzymatic degradation of ECM.\nTumor cells secrete proteolytic enzymes themselves or stimulate macrophages and fibroblasts to secrete these enzymes.\nThe most important proteases are metalloproteinases (MMPs) including collagenase IV.\n\nVascular dissemination and homing of tumor cells\n\nAfter travelling through ECM, tumor cells enter into the vessels.\nIn the vessels, tumor cells tend to aggregate in clumps.\nThis is due to adhesion between tumor cells and blood cells, particularly platelets.\nThis clump is carried away at distant site where it adhere to endothelium, followed by extravasation from the vessels.\nAdhesion to endothelium and further travelling through ECM require same mechanism, as was required initially for attachement and degradation of ECM.\nAt new site, tumor cells proliferate and develops new blood supply → metastatic secondary tumor mass.\nNote → Among adhesion molecule CD44 is of particular interest, which is expressed on normal T-cells and is used by these cells to migrate to selective sites in lymphoid tissue.\n\nAlso know\n\nEzrin is the only metastatis gene, that has been identified till now. It is necessary for metastasis of rhabdomyosarcoma and osteosarcoma.\nIn contrast, several antimetastasis gene have been recognized. The important ones are → NM 23, KAI - 1, Kiss gene.', 'role': 'assistant'}]