Specialized Eukaryotic Cells and Tissues
Cancer is a disease in which cells begin to divide when they shouldn’t, producing masses of cells called tumors. Cancerous tumors are called “malignant” ones because of their ability to grow aggressively, invade surrounding healthy tissue, and “metastasize”, or spread to different locations in the body as tumor cells break off, travel through the blood or lymph, and establish new tumors.
Cancer is generally caused by environmental agents known as “carcinogens”, which include chemicals (such as those found in cigarette smoke) and radiation (like the UV rays of sunlight) that mutate cells, causing them to become cancerous.
Tumors that originate from epithelial cells are generally known as carcinomas, and it is estimated that about 90% of all human cancers are carcinomas. Tumors that originate from muscle tissue are called “sarcomas”, and tumors can also originate from nervous and connective tissues. Epithelial tissue exists in various locations in the body, including the skin, the mucous membranes lining the lungs and gastrointestinal tract, and the linings surrounding major organs.
Which of the following statements is correct?
|A||A tumor located in the liver must be a sarcoma.|
|B||A tumor located in a muscle must be a sarcoma.|
|C||A tumor composed of epithelial cells must be located in an epithelial tissue.|
|D|| A tumor in the breast could theoretically consist of cells of any tissue type.|
Due to the possibility of metastasis, a tumor that originated in one part of the body from a particular type of cell may “spread” to virtually any body location, producing a new tumor there. The tumor, however, will still be made up of the type of cells from which it originally grew.