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Lung
cancer is a malignant tumor of the lungs. Most commonly it is bronchogenic
carcinoma (about 90%).
Lung cancer
is the most lethal malignant tumor
worldwide, causing up to 3 million
deaths.
Exposure to
carcinogens, such as those
present in
tobacco smoke, immediately causes small changes to
the tissue lining the bronchi of the lungs
(the bronchial mucous membrane). This effect is
cumulative, and over time with continued exposure
more and more tissue gets damaged until a lung tumor
develops. If lung tumor grows inwards it may
obstruct the air passageway, causing breathing
difficulties. The lungs may then collapse and
infections can develop, leading to lung abscess. The
patient here would start to cough up blood-stained
material. However,
if the
lung tumor grows outwards in to the lung it may not even
be noticed by the patient before lung
tumor starts to
spread to other parts of the body.
Lung Cancer Symptoms
Early symptoms of
lung cancer can be
similar to those of later signs. Common lung
cancer symptoms
include:
- coughing up
blood
- a bad, chronic
cough
- wheezing
- chest pains
-
weight loss or
loss of appetite
- shortness of
breath
- a hoarse voice
- fatigue
Depending on the
type of tumor, so-called paraneoplastic phenomena
may initially attract attention to the disease. In
lung cancer, this symptom may be Lambert-Eaton
myasthenic syndrome (muscle weakness due to
auto-antibodies), hypercalcemia and SIADH. Tumors in
the top (apex) of the lung, known as Pancoast tumors,
may invade the local part of the sympathetic nervous
system, leading to changed sweating patterns and eye
muscle problems (a combination known as Horner's
syndrome), as well as muscle weakness in the hands
due to invasion of the brachial plexus.
Type of Lung Cancer
There are
two main
types of lung
cancer categorised by the size and appearance of
the malignant cells seen by a histopathologist under
a microscope: small and non-small cell lung cancer.
This classification although based on simple pathomorphological criteria has very important
implications for clinical management and prognosis
of the disease.
Small Cell Lung Cancer
Small cell
carcinoma (also called oat cell carcinoma) is the
less common form of lung cancer, making up 20% of cases. It tends to
start in the
larger breathing tubes and grows rapidly
becoming quite large. The oncogene most commonly
involved is the L-myc. The "oat" cell contains dense
neurosecretory granules which give this an
endocrine/paraneoplastic syndrome association.
Non-small Cell
Lung Cancer
Epidermoid carcinoma
(or Squamous cell carcinoma) also
starts in
the larger breathing tubes but grows slower
meaning that the size of these tumors varies when on
diagnosis.
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