Textbook of Medical-Surgical Nursing 3e

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Unit 3   Applying concepts from the nursing process

Natural killer (NK) cells are a major component of the body’s defence against cancer. NK cells are a subpopulation of lymphocytes that act by directly destroying cancer cells or by producing lymphokines and enzymes that assist in cell destruction. Immune system failure How is it then, that malignant cells can survive and proliferate despite the elaborate immune system defence mechanisms? Several theories suggest how tumour cells can evade an appar- ently intact immune system. If the body fails to recognise the malignant cell as different from ‘self’ (non-self or foreign), the immune response may not be stimulated. When tumours do not possess tumour-associated antigens that label them as foreign, the immune response is not alerted. The failure of the immune system to respond promptly to the malignant cells allows the tumour to grow too large to be managed by normal immune mechanisms. Tumour antigens may combine with the antibodies produced by the immune system and hide or disguise themselves from normal immune defence mechanisms. These tumour antigen- antibody complexes can suppress further production of anti- bodies. Tumours are also capable of changing their appearance or producing substances that impair usual immune responses. These substances not only promote tumour growth but also increase the patient’s susceptibility to infection by various pathogenic organisms. As a result of prolonged contact with a tumour antigen, the patient’s body may be depleted of the specific lymphocytes and no longer able to mount an appropriate immune response. Abnormal concentrations of host suppressor T lymphocytes may play a role in developing cancers. Suppressor T lym- phocytes normally assist in regulating antibody production and diminishing immune responses when they are no longer required. Low levels of serum antibodies and high levels of suppressor cells have been found in patients with multiple myeloma, a cancer associated with hypogammaglobulinaemia (low amounts of serum antibodies). Carcinogens, such as viruses and certain chemicals, including chemothera­peutic agents, may weaken the immune system and ultimately enhance tumour growth. Detection and prevention of cancer In recent years, the Cancer Council Australia, the National Cancer Control Initiative, the Cancer Society of New Zealand, health professionals and researchers have placed greater emphasis on primary and secondary prevention of cancer. Primary prevention is concerned with reducing the risks of cancer in healthy people. Secondary prevention involves detection and screening to achieve early diagnosis and prompt intervention. A diagnosis of cancer today is not the death sentence it used to be; cancer survivorship is now considered a reality. The ability to live beyond the disease has led to a shift in focus, to one that considers the fact that most cancers diag- nosed today will be curable and/or remain a chronic illness. Primary prevention Primary prevention is concerned with reducing the risks of disease through health promotion strategies. It is estimated that almost one third of all cancers worldwide could be pre- vented through primary prevention efforts (Williams-Brown

Hormonal changes with reproduction are also associated with cancer incidence. Early onset of menses under age 12 and delayed onset of menopause after age 55, nulliparity (never giving birth), and delayed childbirth after age 30 are all associ- ated with an increased risk of breast cancer. Increased numbers of pregnancies are associated with a decreased incidence of In humans, malignant cells are capable of developing on a regular basis. Some evidence indicates, however, that the immune system can detect the development of malignant cells and destroy them before cell growth becomes uncontrolled. When the immune system fails to identify and stop the growth of malignant cells, clinical cancer develops. Patients who for various reasons are immunoincompetent have been shown to have an increased incidence of cancer. Organ transplant recipients who receive immunosuppressive therapy to prevent rejection of the transplanted organ have an increased incidence of lymphoma, Kaposi’s sarcoma, squamous cell cancer of the skin, and cervical and anogenital cancers (Herman, Rogers & Ratner, 2007). Patients with immuno­ deficiency diseases, such as AIDS, have an increased incidence of Kaposi’s sarcoma, lymphoma, and rectal and head and neck cancers (Grulich, Vajdic & Cozen, 2007). Some patients who have received alkylating chemotherapeutic agents to treat Hodgkin’s disease have an increased incidence of secondary malignancies (Tward et al., 2007). Autoimmune diseases, such as rheumatoid arthritis and Sjögren’s syndrome, are associated with increased cancer development (Wolf & Michaud, 2007). Finally, age-related changes, such as declining organ function, increased incidence of chronic diseases and diminished immu- nocompetence, may contribute to an increased incidence of cancer in older people. Normal immune responses Normally, an intact immune system has the ability to combat cancer cells in several ways. Usually, the immune system recognises as foreign certain antigens on the cell membranes of many cancer cells. These antigens are known as tumour- associated antigens (also called tumour cell antigens) and are capable of stimulating both cellular and humoral immune responses. Along with the macrophages, T lymphocytes, the soldiers of the cellular immune response, are responsible for recognis- ing tumour-associated antigens. When T lymphocytes recog- nise tumour antigens, other T lymphocytes that are toxic to the tumour cells are stimulated. These lymphocytes proliferate and are released into the circulation. In addition to possessing cytotoxic (cellkilling) properties, T lympho­cytes can stimulate other components of the immune system to rid the body of malignant cells. Certain lymphokines, which are substances produced by lymphocytes, are capable of killing or damaging various types of malignant cells. Other lymphokines can mobilise other cells, such as macrophages, that disrupt cancer cells. Interferon (IFN), a substance produced by the body in response to viral infection, also possesses some antitumour properties. Antibodies produced by B lymphocytes, associated with the humoral immune response, also defend the body against malig- nant cells. These antibodies act either alone or in combination with the complementary system or the cellular immune system. breast, endometrial and ovarian cancers. Role of the immune system