Medical brain notes 15

  DEFINITION In  neoplasia , an abnormal cell or tissue grows more rapidly than normal cells or tissue; it does so by acquiring multiple genetic changes over time and by continuing to grow after the stimuli that initiated the new growth have been removed. EPIDEMIOLOGY Cancer is the  second leading cause of death  in the United States. In 2015, the esti-mated number of new cancers diagnosed was 1,658,370, and the estimated number of deaths from cancer was 589,430. In men,  the sites with the highest new cancer rates are (in order of decreasingfrequency): ·              Prostate ·              Lung and bronchus ·              Colon and rectum These same sites have the highest mortality rate, although lung and bronchus can-cers more commonly cause death than prostate cancer. In women , th...

  CARCINOGENIC AGENTS Chemical carcinogens. Carcinogenesis is a multistep process involving a sequence ofinitiation (mutation) followed by promotion (proliferation). Initiators can be either direct-acting chemical carcinogens (mutagens which cause cancer directly by modi-fying DNA) or indirect-acting chemical carcinogens (procarcinogens which require metabolic conversion to form active carcinogens). Promotors cause cellular prolif-eration of mutated (initiated) cells, which may lead to accumulation of additional mutations. ·              Clinically important chemical carcinogens   are numerous, and include nitro-samines (gastric cancer), cigarette smoke (multiple malignancies), polycyclic aromatic hydrocarbons (bronchogenic carcinoma), asbestos (bronchogenic carcinoma, mesothelioma), chromium and nickel (bronchogenic carcinoma), arsenic (squamous cell carcinomas of skin and lung, angiosarcoma of liver), vinyl chloride...

  CARCINOGENESIS Carcinogenesis  is a multistep process, and development of all human cancersappears to require the accumulation of multiple genetic changes. These changes can involve either inherited germline mutations or acquired mutations. Once a sin-gle severely mutated cell forms, monoclonal expansion of the cell’s line can cause a tumor. Most important mutations in tumorogenesis involve growth promoting genes (proto-oncogenes), growth inhibiting tumor suppressor genes, or the genes regulating apoptosis and senescence. Activation of growth promoting oncogenes. Proto-oncogenes are normal cellulargenes involved with growth and cellular differentiation. Oncogenes are derived from proto-oncogenes by either a change in the gene sequence, resulting in a new gene product (oncoprotein), or a loss of gene regulation resulting in overexpression of the normal gene product. Mechanisms of oncogene activation include point muta-tions, chromosomal translocations, gene amplification, and...

  DIAGNOSIS OF CANCER Histologic diagnosis of cancer. Microscopic examination of tissue or cells is requiredto make the diagnosis of cancer. Material suitable for diagnosis of a tumor may be obtained by complete excision, biopsy, fine needle aspiration, or cytologic smears (Pap test). Immunohistochemistry  may be helpful in confirming the tissue of origin ofmetastatic or poorly differentiated tumors. The technique uses monoclonal antibodies that are specific for a cellular component. Among the many anti-bodies that are clinically useful are:   ·                All of the serum tumor markers   ·                Thyroglobulin (thyroid cancers)   ·                S100 (melanoma and neural tumors)   ·          ...