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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
breast, endometrial and ovarian cancers.
Role of the immune system
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.
