Porth's Essentials of Pathophysiology, 4e

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Cell and Tissue Function

U N I T 1

of cells is determined by the rates of cell proliferation and death by apoptosis. In malignant neoplasms, the accu- mulation of neoplastic cells may result not only from excessive and uncontrolled proliferation, but also from evasion of apoptosis. All tumors—benign and malignant—are composed of two types of tissue: (1) parenchymal or specific func- tional cells of an organ or tissue, and (2) connective tissue that forms the supporting tissue framework or stroma. 2.3 The parenchymal tissue, which is made up of the transformed or neoplastic cells of a tumor, deter- mines its behavior and is the component for which the tumor is named. The supporting nonneoplastic stromal tissue component is made up of connective tissue, extra- cellular matrix, and blood vessels. It is essential to the growth of the tumor since it carries the blood supply and provides support for the parenchymal tumor cells. Terminology Cancers are commonly referred to as tumors or neo- plasms . Although defined in the medical literature as a swelling that can be caused by a number of condi- tions, including inflammation and trauma, the term tumor is increasingly being used to describe a neoplasm. Oncology, from the Greek term onkos, for a “swelling,” refers to the study or science of neoplasms. Clinical oncology deals with neoplastic disorders in the clinical setting, primarily in terms of diagnosis and treatment. Benign tumors usually are named by adding the suf- fix -oma to the parenchymal tissue type from which the growth originated. 2 Thus, a benign epithelial neoplasm of glandular tissue is called an adenoma , and a benign tumor arising in fibrous tissue is called a fibroma . The term car- cinoma is used to designate a malignant tumor of epithe- lial tissue origin. In the case of malignancies that originate from glandlike structures, the term adenocarcinoma is used, and for those that originate from squamous cells, the term squamous cell carcinoma is used. Malignant tumors of mesenchymal origin are called sarcomas . A cancer of fibrous tissue is a fibrosarcoma and a malignant tumor composed of chondrocytes is a chondrosarcoma. Papillomas are benign microscopic or macroscopic fingerlike projections that grow on any surface. A polyp is a growth that projects from a mucosal surface, such as the intestine. Although the term usually implies a benign neoplasm, some malignant tumors also appear as pol- yps. Adenomatous polyps are considered precursors to adenocarcinomas of the colon. Table 7-1 lists the names and tissue types of selected benign and malignant tumors.

Estimated New Cases

Prostate (28%) Lung and bronchus (14%) Colon and rectum (9%) Urinary bladder (6%) Melanoma of the skin (5%) Kidney and renal pelvis (5%) Non-Hodgkin lymphoma (4%) Leukemia (3%) Oral cavity and pharynx (3%) Pancreas (3%) Lung and bronchus (28%) Prostate (10%) Colon and rectum (9%) Pancreas (6%) Liver and intrahepatic bile duct (5%) Leukemia (4%) Esophagus (4%) Urinary bladder (4%) Non-Hodgkin lymphoma (3%) Kidney and renal pelvis (3%)

Breast (29%) Lung and bronchus (14%) Colon and rectum (9%) Uterine corpus (6%) Thyroid (6%) Non-Hodgkin lymphoma (4%) Melanoma of the skin (4%) Ovary (3%) Kidney and renal pelvis (3%) Pancreas (3%)

Estimated Deaths

Lung and bronchus (26%) Breast (14%) Colon and rectum (9%) Pancreas (7%) Ovary (5%) Leukemia (4%) Non-Hodgkin lymphoma (3%) Uterine corpus (3%) Brain and other

nervous system (2%) Liver and intrahepatic bile duct (2%)

adaptive mechanism for cell replacement when old cells die or additional cells are needed. Fundamental to the origin of all neoplasms are the genetic changes that allow excessive and uncontrolled proliferation that is unregu- lated by normal growth-regulating stimuli to occur. Differentiation is the process of specialization whereby new cells acquire the structural, microscopic, and func- tional characteristics of the cells they replace. Neoplasms are commonly classified as benign or malignant. Benign neoplasms are composed of well-differentiated cells that resemble the normal counterpart both in terms of struc- ture and function but have lost the ability to control cell proliferation. Malignant neoplasms are less differentiated and have lost the ability to control both cell differentia- tion and proliferation. In general, the better the differen- tiation of a neoplasm, the slower its rate of growth and the more completely it retains the functional capabilities found in its normal counterparts. For example, benign neoplasms and even well-differentiated cancers of endo- crine glands frequently elaborate the hormones charac- teristic of their origin. Apoptosis , which is discussed in Chapter 2, is a form of programmed cell death that eliminates senescent cells, deoxyribonucleic acid (DNA), and damaged or unwanted cells. In adult tissues, the size of a population *Excludes basal and squamous cell skin cancers and in situ carcinomas except urinary bladder. Note: Estimates are rounded to the nearest 10. FIGURE 7-1. Ten leading cancer types for the estimated new cancer cases and deaths in the United States by sex and site, 2013. (Adapted from Siegel R, Naishadham D, Jemel A. Cancer statistics, 2013. CA Cancer J Clin. 2013;63[1]:11–30.)

Biology of Benign and MalignantTumors

The differences between benign and malignant tumors are determined by (1) the characteristics of the tumor cells, (2) the rate of growth, (3) local invasion, and (4) the ability to metastasize. The characteristics of benign and malignant neoplasms are summarized in Table 7-2.