Predisposing Factors

Predisposing factors, also called risk factors, make a person or group more vulnerable to disease. Although the recognition of risk factors may be significant in prevention, diagnosis, and prognosis, it does not precisely predict the occurrence of disease, nor does the absence of predisposing factors necessarily protect against the development of disease. A person may be susceptible to a greater or lesser degree, due to one or more risk factors that overlap or occur in combination. Predisposing factors include age, gender, lifestyle, environment, and heredity.

Inflammation and Repair

Injury and disease impose stress on the body’s equilibrium and disrupt or destroy cellular function. Acute inflammation, a normal protective physiologic response to tissue injury and disease, is accompanied by redness, heat, swelling, pain, and loss of function. Widespread inflammation is marked by systemic symptoms, such as fever, malaise, and loss of appetite. Blood testing may reveal an elevated white blood cell count or an elevated erythrocyte sedimentation rate (ESR). C-reactive protein (CRP) is a blood test marker used to detect inflammatory disorders, among other pathologies. The intensity of inflammation depends on the cause, the area of the body involved, and the physical condition of the person. An inflammatory response is considered a nonspecific immune response. Infection with pathogens, the effects of toxins, physical trauma, ischemia, and necrosis are some conditions that induce the inflammatory response. E1-1

Acute inflammation, an exudative response, attempts to wall off, destroy, and digest bacteria and dead or foreign tissue. Vascular changes allow fluid to leak into the site; this fluid contains chemicals that permit phagocytic activity by white blood cells. The process prevents the spread of infection through antibody action and other chemicals released by cells with more specific immune activity. After the mechanisms of inflammation have contained the insult and “cleaned up” the damaged area, repair and replacement of tissue can begin (Figure 1-1). A normal inflammatory response can be inhibited by immune disorders, chronic illness, or the use of certain medications, especially long-term steroid therapy.

When an inflammatory response is chronic or too intense, damage to the affected tissue can result, thereby inhibiting the healing process. Diseases with a chronic inflammation component include arthritis, asthma, and eczema.

Infection

Infectious diseases are caused by pathogens. The cardinal signs of local infection are redness, swelling, heat, pain, fever, pus, enlarged lymph glands, and red streaks. Symptoms of widespread infection are fever, headache, body aches, weakness, fatigue, loss of appetite, and delirium.

When disease-causing organisms find ideal conditions in which to grow and multiply in the body, they cause disease by (1) invasion and local destruction of living tissue and (2) intoxication or production of substances that are poisonous to the body. The result is tissue damage that has the potential for producing systemic involvement.

The sources of infection can be endogenous (originating within the body) or exogenous (originating outside the body). Modes of transmission of pathogenic organisms are direct or indirect physical contact, inhalation or droplet nuclei, ingestion of contaminated food or water, or inoculation by an insect or animal. Pathogenic agents include bacteria, viruses, fungi, and protozoa (Table 1-1). E1-2

A communicable or contagious disease can be transmitted directly from one person to another. Carriers are asymptomatic persons or animals that harbor in their bodies pathogens that can be transferred to others.

The body’s natural defense systems against infection include (1) natural mechanical and chemical barriers, such as the skin, the cilia, body pH, and normal body flora; (2) the inflammatory response; and (3) the immune response. When these mechanisms of defense fail to contain or eliminate infection, appropriate and prompt medical intervention is required to treat the host and to control transmission of the infectious disease. This is accomplished by first isolating and identifying the organism through laboratory testing. Subsequently, appropriate antimicrobial therapy using antibiotic (antibacterial), antifungal, antiparasitic, or antiviral agents can begin. Analgesics for pain and antipyretic agents for fever, as well as other comfort measures, are dispensed. Adequate fluid intake, infection control measures, and rest are important for management.

Fundamental to preventing the spread of certain infections are isolation of the infected individual when necessary, implementation of immunization programs, and rudimentary public health teaching. To facilitate early intervention and infection control measures, many infectious diseases such as encephalitis, syphilis, and tuberculosis must be reported to the local health department. The Centers for Disease Control and Prevention (CDC) publishes notifiable diseases in the United States. In hospitals, the control of postsurgical bacterial wound infections relies on breaking the chain of transmission by killing the pathogen, isolating infected persons, and using precautions such as hand washing and sterilization to prevent cross-contamination.

Of special concern is the emergence of new, virulent antibiotic-resistant strains of bacteria (commonly referred to as “superbugs”), which present a danger even to the young and healthy. Methicillin-resistant strains of Staphylococcus aureus (MRSA) are showing up in hospitals, jails, crowded living quarters, and other community environments. MRSA is to blame for aggressive skin and soft tissue infections, sometimes mistaken for spider bites; these lesions quickly develop into abscesses and cellulitis. In addition to skin infections, MRSA can cause fatal pneumonia, bone infections, and septicemia. Many MRSA strains of bacteria are currently resistant to several different antibiotics. Occasionally toxic and resistant strains of MRSA have been termed “flesh eating bacteria” because of the rapid spread of infection resulting in destruction of human skin. MRSA is a leading cause of surgical wound infections in hospitals. The pathogen is easily transmitted from person to person and can survive for a long time nearly anywhere in the environment. About 1 in 100 persons in the United States have the organisms in their body without showing signs of infection; however, they may transmit MRSA bacteria to others. Healthy persons are at lower risk for infection. Because of the constant threat of infection, everyone must be considered a risk for MRSA, particularly hospital patients. Fortunately a few antibiotics do exist that are effective against strains of MRSA, but they are used judiciously to prevent emergence of new antibiotic-resistant strains. Excellent hygiene practices help prevent the spread of MRSA. Stricter infection control measures throughout U.S. health care systems have reduced MRSA infections significantly. Participating medical facilities have implemented active surveillance testing such as nasal swab tests upon patient admission. Public education stresses thorough and frequent handwashing across the board as an effective practice of infection control in the community as well. Vancomycin-resistant enterococcal (VRE) is an increasing problem in chronic care facilities and hospitals because there are only a few antibiotics that can be used to treat VRE. This resistant bacterial infection is spread from person to person and can cause many types of infection.

Genetic Diseases

Every cell in the body is coded with genetic information arranged on 23 pairs of chromosomes; one chromosome from each pair is inherited from the father and the other from the mother. The X and Y chromosomes are known as the sex chromosomes, whereas the remaining 22 pairs are called autosomes. Each cell in an individual’s body contains the same chromosomes and genetic code (genotype). A karyotype is an ordered arrangement of photographs of a full chromosome set (Figure 1-2). Genes, the basic units of heredity, are small stretches of a DNA (deoxyribonucleic acid) molecule, situated at a particular site on a chromosome.

Genetic diseases are (1) produced by an abnormality in, or a mutation of, the genetic code in a single gene; (2) caused by several abnormal genes (producing so-called polygenic diseases); or (3) caused by the abnormal presence or absence of an entire chromosome; or (4) caused by alteration in the structure of chromosomes. Harmful genetic mutations, or changes in the genetic code, passed from one generation to the next may occur spontaneously or be caused by agents known to disrupt the normal sequence of DNA units. Agents (called mutagens) that can damage DNA include certain chemicals, radiation, and viruses.

The main modes of inheritance for genetic diseases are as follows:

Autosomal dominant—the gene in question is located on an autosome and the mutant phenotype is seen even if a normal gene is present on the other chromosome in the pair. Examples include Marfan’s syndrome and Huntington’s disease.

Autosomal recessive—the gene is located on an autosome but is insufficient to produce the mutant phenotype in the presence of a normal gene on the paired chromosome. Both genes must be mutated for disease to occur. Examples include cystic fibrosis and phenylketonuria.

X-linked (sex-linked) recessive—the gene is located only on the X chromosome. Males are much more commonly affected by these diseases than are females. Examples include Duchenne’s muscular dystrophy and hemophilia A.

Individuals who have only one copy of a recessive gene and appear outwardly normal are known as carriers of the defective gene. The mutant gene may produce an abnormal protein that causes a disease, or it may fail to produce its normal cellular function. Hereditary diseases often are noted at birth, but they may not appear until later in life. Many genetic mutations are compatible with life, but some are not.

The following examples of genetic abnormalities are discussed in this book:

Genetic Counseling

For many genetic diseases, the responsible gene or chromosomal abnormality has been identified, and it is possible to test for the presence of the mutation in an individual. The discovery of a genetic disease in a family member often raises the questions of whether other family members are affected, whether others are carriers of the disease, and whether future offspring will be affected by it. Genetic counseling is a communication process that is centered on the occurrence or risk of occurrence of a genetic disorder in a family. Such counseling should be offered to all families affected by the diagnosis of a genetic disease in one or more members.

Genetic counseling is more than simply reproductive counseling concerning inherited disorders; it helps to bridge the gap between complicated medical and scientific concepts and the emotional aspects of being diagnosed with a certain condition. Attending physicians and other counselors help the family understand the diagnosis, course of disease, and available treatment options. They talk about heredity and risk of occurrence in other family members and future offspring. If genetic testing is available for the disorder, the counselors first explain the test and the benefits of taking or not taking the test. They help prepare the family for any outcome of the genetic test. Common feelings experienced after receiving a diagnosis of a genetic disorder are a sense of being “labeled,” guilt that other family members may be affected, worry about insurance discrimination, or a sense of hopelessness if the disease has no cure. Even if the patient receives the “good” news that he or she is not affected, there may be a feeling of “survivor guilt.” With the increase in availability of genetic testing for many conditions, genetic counselors are usually available at most major hospitals.

Cancer

Note: What follows is a general introduction to the pathology and pathogenesis of cancer, including prognosis as demonstrated by staging and grading of tumors. Broad measures of prevention, diagnosis, and treatment are also discussed. Current statistics are included. Specific sites and types of cancers are addressed in subsequent chapters.

Cancer, a leading cause of death in the United States, refers to a group of diseases characterized by uncontrolled cell proliferation. This abnormal growth leads to the development of tumors or neoplasms, a relentlessly growing mass of abnormal cells that proliferates at the expense of the healthy organism. Tumors are characterized as malignant or benign and according to the cell type and tissue of origin (Tables 1-2 and 1-3). Some of the main general types of cancer are carcinoma, cancer of the epithelial cells; sarcoma, cancer of the supportive tissues of the body, such as bone and muscle; lymphoma, cancer arising in the lymph nodes and tissues of the immune system; leukemia, cancer of blood cell precursors; and melanoma, cancer of the melanin-producing cells of the body.

TABLE 1–2 Comparison of Benign and Malignant Tumors

CHARACTERISTICS	BENIGN	MALIGNANT
Mode of growth	Relatively slow growth by expansion; encapsulated; cells adhere to each other	Rapid growth; invades surrounding tissue by infiltration
Cells under microscopic examination	Resemble tissue of origin; well differentiated; appear normal	Do not resemble tissue of origin; vary in size and shape; abnormal appearance and function
Spread	Remains localized	Metastasis; cancer cells carried by blood and lymphatics to one or more other locations; secondary tumors occur
Other properties	No tissue destruction; not prone to hemorrhage; may be smooth and freely movable	Ulceration and/or necrosis; prone to hemorrhage; irregular and less movable
Recurrence	Rare after excision	A common characteristic
Pathogenesis	Symptoms related to location with obstruction and/or compression of surrounding tissue or organs; usually not life-threatening unless inaccessible	Cachexia; pain; fatal if not controlled

Gross appearance of benign (A) and malignant (B) tumors.

Benign tumors develop slowly and can arise from any tissue. They tend to remain encapsulated and do not infiltrate surrounding tissue. When examined microscopically, benign tumor cells are well differentiated—they resemble the tissue of origin. Because tumors take up space, complications can result from compression of tissue by the lesion or obstruction of organs. Benign tumors rarely recur after surgical removal.

Malignant tumors can represent a serious threat to the life and well-being of a person. Cancer cells are variable in appearance and disorderly (anaplastic) with irreversible changes in structure. They are usually poorly differentiated and do not resemble the tissue of origin. Malignant tumors have the ability to invade the surrounding tissue. Often malignant cells enter the bloodstream or the lymphatic vessels and lead to tumor growth in other areas of the body. These secondary tumors are known as metastases. Metastasis makes the neoplasm more difficult to eradicate from the body.

Cancer is actually many different diseases with numerous causes. Cancer may be caused by both external exposure to carcinogens (chemicals, radiation, and viruses) and internal factors (hormones, immune conditions, and inherited mutations). Ten years or longer may pass between exposures or mutations and the onset of detectable cancer. Cancer can develop in anyone, but the frequency increases with age. Figure 1-3 shows the leading sites of cancer incidence and death.

(Reprinted with permission of the American Cancer Society, Inc., Cancer Facts and Figures-2006.) American Cancer Society

Recommendations for decreasing the risk of cancer encompass guidelines and appropriate screening tests for early detection and treatment. Primary prevention guidelines include the following:

The diagnosis of cancer is very prevalent in U.S. society. Statistics from the American Cancer Society estimate that nearly 1.5 million Americans are diagnosed with invasive cancer and more than 500,000 die of cancer every year. One out of every four deaths in the United States is cancer-related.

Cancer detection employs general and specific techniques of physical examination, medical history-taking, and laboratory screening tests. Screening examinations can detect cancers of the breast, rectum, colon, prostate, cervix, testis, tongue, mouth, and skin early, when treatment is more likely to succeed. These cancers account for approximately half of all new cancer cases.

Some tumor cells produce and secrete substances called tumor markers. Screening tests for elevation of blood serum levels of tumor markers, when considered with other diagnostic data, are shown to have clinical value in (1) helping determine the diagnosis of cancer and (2) evaluating response to therapy. For example, in primary and metastatic prostate cancer, elevated prostate-specific antigen (PSA) may be found.

If cancer is suspected, additional diagnostic investigation is achieved by using high technology imaging techniques and, most decisively, by obtaining a biopsy of the lesion.

After a cancer diagnosis has been confirmed, the patient undergoes an evaluation to determine the stage of the neoplasm. The stage reflects tumor size and the extent of tumor spread. It has important implications for determining the choice of treatment options and prognosis. Staging is a method that institutions can use to communicate patient information, so the procedures and staging systems used for staging must be standardized worldwide. Types of cancer that are more prevalent in less-developed countries, such as cervical cancer, are often staged clinically and without use of technologies such as magnetic resonance imaging (MRI) and computed tomography (CT) scans. For some types of cancer, such as endometrial neoplasms, complete staging requires surgical removal of the affected organ and examination of the specimen by an experienced pathologist.

Although a number of different staging systems exist, the majority of cancers use a TNM system. TNM staging assesses the neoplasm in three different areas: the size or extent of the primary tumor (T), the extent of regional lymph node involvement by the tumor (N), and the number of distant metastases (M). Once all three parameters are defined, they are combined to assign a stage number of I, II, III, or IV to the cancer. One is an early stage tumor and carries the best prognosis, whereas IV is the most advanced stage. Within each stage, subcategories are defined (Ia, Ib, etc.) to further aid in treatment planning and facilitation of communication between institutions and physicians. See Table 1-4 for an example of staging.

TABLE 1–4

Melanoma Staging System of the American Joint Committee on Cancer

PRIMARY TUMOR (pT)
pTX	Primary tumor cannot be assessed.
pTO	No evidence of primary tumor
pTis	Melanoma in situ (atypical melanotic hyperplasia, severe melanotic dysplasia), not an invasive lesion (Clark’s Level I)
pT1	Tumor 0.75 mm or less in thickness and invades the papillary dermis (Clark’s Level III)
pT3	Tumor more than 1.5 mm but not more than 4 mm in thickness and/or invades the reticular dermis (Clark’s Level IV)
pT3a	Tumor more than 1.5 mm but not more than 3 mm in thickness
pT3b	Tumor more than 3 mm but not more than 4 mm in thickness
pT4	Tumor more than 4 mm in thickness and/or invades the subcutaneous tissue (Clark’s Level V) and/or satellite(s) within 2 cm of the primary tumor
pT4a	Tumor more than 4 mm in thickness and/or invades the subcutaneous tissue
pT4b	Satellite(s) within 2 cm of primary tumor
LYMPH NODE (N)
NX	Regional lymph nodes cannot be assessed.
NO	No regional lymph node metastasis
N1	Metastasis 3 cm or less in greatest dimension in any regional lymph nodes
N2	Metastasis more than 3 cm in greatest dimension in any regional lymph node(s) and/or in-transit metastasis
N2a	Metastasis more than 3 cm in greatest dimension in any regional lymph node(s)
N2b	In-transit metastasis
N2c	Both (N2a and N2b)
DISTANT METASTASIS (M)
MX	Presence of distant metastasis cannot be assessed.
MO	No distant metastasis
M1	Distant metastasis
M1a	Metastasis in skin or subcutaneous tissue of lymph node(s) beyond the regional lymph nodes
M1b	Visceral metastasis
STAGE GROUPING
Stage I	pT1, pT2	NO	MO
		NO	MO
Stage II	pT3	NO	MO
Stage III	pT4, Any pT	NO	MO
		N1, N2	MO
Stage IV	Any pT	Any N	M1

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