144
U N I T 1
Cell and Tissue Function
(HTLV-1) is the only known retrovirus to cause cancer in
humans. Human T-cell leukemia virus-1 is associated with
a form of T-cell leukemia that is endemic in certain parts
of Japan and some areas of the Caribbean and Africa,
and is found sporadically elsewhere, including the United
States and Europe.
2
Similar to the AIDS virus, HTLV-1 is
attracted to the CD4
+
T cells, and this subset of T cells is
therefore the major target for malignant transformation.
The virus requires transmission of infected T cells by way
of sexual intercourse, infected blood, or breast milk.
Clinical Manifestations
There probably is not a single body function left unaf-
fected by the presence of cancer. Even the presenting
signs and symptoms may be localized or widespread.
Local and Regional Manifestations
Because tumor cells replace normally functioning paren-
chymal cells, the initial manifestations of cancer usually
reflect the function of the primary site of involvement.
For example, lung cancer initially produces impairment
of respiratory function; as the tumor grows and metas-
tasizes, other body structures become affected.
Cancer has no regard for normal anatomic bound-
aries; as it grows, it invades and compresses adjacent
structures. Abdominal cancer, for example, may com-
press the viscera and cause bowel obstruction. Growing
tumors may also compress and erode blood vessels,
causing ulceration and necrosis along with frank bleed-
ing and sometimes hemorrhage.
The development of effusions (i.e., fluid) in the pleu-
ral, pericardial, or peritoneal spaces may be the present-
ing sign of some tumors. Direct involvement of the serous
surface seems to be the most significant inciting factor,
although many other mechanisms such as obstruction of
lymphatic flow may play a role. Most persons with pleu-
ral effusions are symptomatic at presentation with chest
pain, shortness of breath, and cough. More than any
other malignant neoplasms, ovarian cancers are asso-
ciated with the accumulation of fluid in the peritoneal
cavity. Complaints of abdominal discomfort, swelling
and a feeling of heaviness, and increase in abdominal
girth, which reflect the presence of peritoneal effusions
or ascites, are the most common presenting symptoms in
ovarian cancer, occurring in up to 65% of women with
the disease.
33
Systemic Manifestations
Cancer also produces systemic manifestations such as
anemia, anorexia and cachexia, and fatigue and sleep dis-
orders. Many of these manifestations are compounded
by the side effects of methods used to treat the disease. In
its late stages, cancer often causes pain (see Chapter 35).
Pain is probably one of the most dreaded aspects of can-
cer, and pain management is one of the major treatment
concerns for persons with incurable cancers. Although
research has produced amazing insights into the causes
and cures for cancer, only recently have efforts focused
on the associated side effects of the disease.
Anemia
Anemia is common in persons with various types of
cancers. It may be related to blood loss, iron deficiency,
hemolysis, impaired red cell production, or treatment
effects.
34–36
For example, drugs used in treatment of
cancer are cytotoxic and can decrease red blood cell
production. Also, there are many mechanisms through
which erythrocyte production can be impaired in
persons with malignancies including nutritional defi-
ciencies, bone marrow failure, a blunted erythro-
poietin response to hypoxia, and an iron deficiency.
Inflammatory cytokines generated in response to
tumors decrease erythropoietin synthesis, resulting in a
decrease in erythrocyte production. Iron deficiency may
SUMMARY CONCEPTS
■■
The etiology of cancer is highly complex,
encompassing both molecular and cellular
origins, and external and contextual factors
such as heredity and environmental agents that
influence its inception and growth. It is likely that
multiple factors interact at the molecular and
cellular level to transform normal cells into cancer
cells.
■■
The molecular pathogenesis of cancer is
thought to have its origin in genetic damage or
a mutation that changes the cell’s physiology
and transforms it into a cancer cell.The types of
genes involved in cancer are numerous, but two
main groups are the proto-oncogenes, which
control cell growth and replication, and tumor-
suppressor genes, which are growth-inhibiting
regulatory genes.
■■
Genetic and molecular mechanisms that increase
susceptibility to cancer and/or facilitate cancer
include defects in DNA repair mechanisms,
defects in growth factor signaling pathways,
evasion of apoptosis, development of sustained
angiogenesis, invasion, and metastasis. Genetic
and epigenetic damage may be the result of
interactions between multiple risk factors or
repeated exposure to a single carcinogenic
(cancer-producing) agent.
■■
Among the external and contextual risk factors
that have been linked to cancer are heredity,
hormonal factors, obesity, immunologic
mechanisms, and environmental agents such as
chemicals, radiation, and cancer-causing viruses
and microbes.
