146
U N I T 1
Cell and Tissue Function
hematologic complications.
47
For example, a variety
of cancers may produce procoagulation factors that
contribute to an increased risk for venous thrombosis
and nonbacterial thrombotic endocarditis. Sometimes,
unexplained thrombotic events are the first indication
of an undiagnosed malignancy. The precise relation-
ship between coagulation disorders and cancer is still
unknown.Severalmalignancies,suchasmucin-producing
adenocarcinomas, release thromboplastin and other
substances that activate the clotting system.
The symptomatic paraneoplastic neurologic dis-
orders are relatively rare with the exception of the
Lambert-Eaton myasthenic syndrome, which affects
about 3% of persons with small cell lung cancer, and
myasthenia gravis, which affects about 15% of people
with thymoma.
48,49
The
Lambert-Eaton syndrome
, or
reverse myasthenia gravis, is seen almost exclusively in
small cell lung cancer. It produces muscle weakness in
the limbs rather than the initial mouth and eye muscle
weakness seen in myasthenia gravis. The origin of para-
neoplastic neurologic disorders is thought to be immune
mediated. The altered immune response is initiated by
the production of onconeural antigens (e.g., antigens
normally expressed in the nervous system) by the can-
cer cells. The immune system, in turn, recognizes the
onconeural antigens as foreign and mounts an immune
response. In many cases, the immune attack controls the
growth of the cancer.
The paraneoplastic syndromes may be the earliest
indication that a person has cancer, and should be
regarded as such. They may also represent significant
clinical problems, may be potentially lethal in persons
with cancer, and may mimic metastatic disease and con-
found treatment. Diagnostic methods focus on both
identifying the cause of the disorder and locating the
malignancy responsible. Techniques for precise identifi-
cation of minute amounts of polypeptides may allow for
early diagnosis of curable malignancies in asymptomatic
individuals. The treatment of paraneoplastic syndromes
involves concurrent treatment of the underlying cancer
and suppression of the mediator causing the syndrome.
TABLE 7-3
Common Paraneoplastic Syndromes
Type of Syndrome
AssociatedTumorType
Proposed Mechanism
Endocrinologic
Syndrome of inappropriate ADH
Small cell lung cancer, others
Production and release of ADH by tumor
Cushing syndrome
Small cell lung cancer, bronchial
carcinoid cancers
Production and release of ACTH by tumor
Hypercalcemia
Squamous cell cancers of the lung,
head, neck, ovary
Production and release of polypeptide
factor with close relationship to PTH
Hematologic
Venous thrombosis
Pancreatic, lung, other cancers
Production of procoagulation factors
Nonbacterial thrombolytic
endocarditis
Advanced cancers
Neurologic
Eaton-Lambert syndrome
Small cell lung cancer
Autoimmune production of antibodies to
motor end-plate structures
Myasthenia gravis
Thymoma
Dermatologic
Acanthosis nigricans
Gastric carcinoma
Possibly caused by production of growth
factors (epidermal) by tumor cells
ACTH, adrenocorticotropic hormone; ADH, antidiuretic hormone; PTH, parathyroid hormone.
SUMMARY CONCEPTS
■■
There probably is no single body function left
unaffected by the presence of cancer. Because
tumor cells replace normally functioning
parenchymal tissue, the initial manifestations
of cancer usually reflect the primary site of
involvement.
■■
Cancer compresses blood vessels, obstructs
lymph flow, disrupts tissue integrity, invades
serous cavities, and compresses visceral organs.
It may result in development of effusions (i.e.,
fluid) in the pleural, pericardial, or peritoneal
spaces.
■■
Systemic manifestations of cancer include
anorexia and cachexia; fatigue and sleep
disorders; and anemia.
■■
Cancer may also produce paraneoplastic
syndromes that arise from the ability of
neoplasms to elaborate hormones and other
chemical mediators to produce endocrine,
hematopoietic, neurologic, and dermatologic
syndromes. Many of these manifestations are
compounded by the side effects of methods used
to treat the disease.
