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Chapter 24: Cancer. Tumor Cells and the Onset of Cancer. Tumors. Benign – non cancerous abnormality ex: wart fibrous capsule usually delineates the extent of a benign tumor Become serious medical problems only if their size interferes with normal functions
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Chapter 24: Cancer Tumor Cells and the Onset of Cancer
Tumors • Benign – non cancerous abnormality ex: wart fibrous capsule usually delineates the extent of a benign tumor Become serious medical problems only if their size interferes with normal functions or if they secrete excess amounts of biologically active substances like hormones
Tumors cont… • Malignant – cancerous abnormality High fraction of cells grow and divide rapidly. Invade surrounding tissues and set up areas of proliferation away from the original site. The spread of tumors and establishments of secondary growth is called metastasis.
Tumors cont… • Cancer cells can be distinguished from normal cells by microscopic examination. • Malignant cells are characterized by large nucleuses,prominent nucleoli, and little specialized structure.
Malignant Tumors • Classification: Carcinomas – derived from endoderm or ectoderm. Sarcomas – derived from mesodern. Leukemias – class of sarcoma, grow as individual cells in the blood.
Tumors and Blood Vessels • Tumors require new blood vessels in order to grow to a large mass. • Most tumors induce the formation of new blood vessels that invade the tumor and nourish it, through a process called angiogenesis.
Cancer Development • Multiple mutations are required for cancer to form. • A mutation in one cell would give it a slight growth advantage. • One of its progeny cells would then undergo a second mutation that would allow its descendents to grow uncontrollaby and form a benign tumor.
Cancer Development cont… • A third mutation in a cell within the tumor would allow it to outgrow the others, and its progeny would form a mass of cell, each containing all three mutations. • An additional mutation in one of these cells would allow its progeny to escape into the blood and establish daughter colonies at other sites.
Review • Tumors may be benign or malignant. • Malignant tumors are differentiated from benign tumors by their invasiveness and spread. • Tumors require new blood vessels to grow. • Multiple mutations must occur for cancer to form.