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Cancer >> Lung
| Q. 1: What is
cancer of the lung?
|Q. 2: How common
is lung cancer?
|Q. 3: What causes
|Q. 4: What are
the types of lung cancer?
|Q. 5: What are
the signs and symptoms of lung cancer?
|Q. 6: Does lung
cancer run in families?
Q. 1 : What is
cancer of the lung?
Cancer of the lung, like all
cancers, results from an abnormality in the body's
basic unit of life, the cell. Normally, the body
maintains a system of checks and balances on cell
growth so that cells divide to produce new cells
only when needed. Disruption of this system of
checks and balances on cell growth results in
an uncontrolled division and proliferation of
cells that eventually forms a mass known as a
Tumors can be benign or malignant; when we
speak of "cancer," we refer to those
tumors that are considered malignant. Benign
tumors can usually be removed and do not spread
to other parts of the body. Malignant tumors,
on the other hand, grow aggressively and invade
other tissues of the body, allowing entry of
tumor cells into the bloodstream or lymphatic
system and then to other sites in the body.
This process of spread is termed metastasis;
the areas of tumor growth at these distant sites
are called metastases. Since lung cancer tends
to spread or metastasize very early in its course,
it is a very life-threatening cancer and one
of the most difficult cancers to treat. While
lung cancer can spread to any organ in the body,
certain organs -- particularly the adrenal glands,
liver, brain, and bone -- are the most common
sites for lung-cancer metastasis.
The lung is also a very common site for metastasis
from tumors in other parts of the body. Tumor
metastases are made up of the same type of cells
as the original, or primary, tumor. For example,
if prostate cancer spreads via the bloodstream
to the lungs, it is metastatic prostate cancer
in the lung and is not lung cancer.
Q. 2 : How common is lung cancer?
Lung cancer is responsible
for the most cancer deaths in both men and women
throughout the world. The American Cancer Society
estimates that 215,020 new cases of lung cancer
in the U.S. will be diagnosed and 161,840 deaths
due to lung cancer will occur in 2008. According
to the U.S. National Cancer Institute, approximately
one out of every 14 men and women in the U.S.
will be diagnosed with cancer of the lung or airways
at some point in their lifetime.
Lung cancer is predominantly a disease of the
elderly; almost 70% of people diagnosed with
the condition are over 65 years of age, while
less than 3% of cases occur in people under
Lung cancer was not common prior to the 1930s
but increased dramatically over the following
decades as tobacco smoking increased. In many
developing countries, the incidence of lung
cancer is beginning to fall following public
education about the dangers of cigarette smoking
and effective smoking-cessation programs. Nevertheless,
lung cancer remains among the most common types
of cancers in both men and women worldwide.
Lung cancer has also surpassed breast cancer
in causing the most cancer-related deaths in
women in the United States.
Q. 3 : What causes
The incidence of lung cancer is strongly
correlated with cigarette smoking, with about
90% of lung cancers arising as a result of tobacco
use. The risk of lung cancer increases with the
number of cigarettes smoked over time; doctors
refer to this risk in terms of pack-years of smoking
history (the number of packs of cigarettes smoked
per day multiplied by the number of years smoked).
For example, a person who has smoked two packs
of cigarettes per day for 10 years has a 20 pack-year
smoking history. While the risk of lung cancer
is increased with even a 10-pack-year smoking
history, those with 30-pack-year histories or
more are considered to have the greatest risk
for the development of lung cancer. Among those
who smoke two or more packs of cigarettes per
day, one in seven will die of lung cancer.
Pipe and cigar smoking can also cause lung
cancer, although the risk is not as high as
with cigarette smoking. While someone who smokes
one pack of cigarettes per day has a risk for
the development of lung cancer that is 25 times
higher than a nonsmoker, pipe and cigar smokers
have a risk of lung cancer that is about five
times that of a nonsmoker.
Tobacco smoke contains over 4,000 chemical
compounds, many of which have been shown to
be cancer-causing, or carcinogenic. The two
primary carcinogens in tobacco smoke are chemicals
known as nitrosamines and polycyclic aromatic
hydrocarbons. The risk of developing lung cancer
decreases each year following smoking cessation
as normal cells grow and replace damaged cells
in the lung. In former smokers, the risk of
developing lung cancer begins to approach that
of a nonsmoker about 15 years after cessation
Passive smoking, or the inhalation of tobacco
smoke from other smokers sharing living or working
quarters, is also an established risk factor
for the development of lung cancer. Research
has shown that nonsmokers who reside with a
smoker have a 24% increase in risk for developing
lung cancer when compared with other nonsmokers.
An estimated 3,000 lung cancer deaths occur
each year in the U.S. that are attributable
to passive smoking.
Asbestos fibers are silicate fibers that can
persist for a lifetime in lung tissue following
exposure to asbestos. The workplace is a common
source of exposure to asbestos fibers, as asbestos
was widely used in the past as both thermal
and acoustic insulation. Today, asbestos use
is limited or banned in many countries, including
the U.S. Both lung cancer and mesothelioma (cancer
of the pleura of the lung as well as of the
lining of the abdominal cavity called the peritoneum)
are associated with exposure to asbestos. Cigarette
smoking drastically increases the chance of
developing an asbestos-related lung cancer in
exposed workers. Asbestos workers who do not
smoke have a fivefold greater risk of developing
lung cancer than nonsmokers, and those asbestos
workers who smoke have a risk that is 50 to
90 times greater than nonsmokers.
Radon gas is a natural, chemically inert gas
that is a natural decay product of uranium.
Uranium decays to form products, including radon,
that emit a type of ionizing radiation. Radon
gas is a known cause of lung cancer, with an
estimated 12% of lung-cancer deaths attributable
to radon gas, or 15,000-22,000 lung-cancer-related
deaths annually in the U.S., making radon the
second leading cause of lung cancer in the U.S.
As with asbestos exposure, concomitant smoking
greatly increases the risk of lung cancer with
radon exposure. Radon gas can travel up through
soil and enter homes through gaps in the foundation,
pipes, drains, or other openings. The U.S. Environmental
Protection Agency estimates that one out of
every 15 homes in the U.S. contains dangerous
levels of radon gas. Radon gas is invisible
and odorless, but it can be detected with simple
While the majority of lung cancers are associated
with tobacco smoking, the fact that not all
smokers eventually develop lung cancer suggests
that other factors, such as individual genetic
susceptibility, may play a role in the causation
of lung cancer. Numerous studies have shown
that lung cancer is more likely to occur in
both smoking and nonsmoking relatives of those
who have had lung cancer than in the general
population. Recent research has localized a
region on the long (q) arm of human chromosome
number 6 that is likely to contain a gene that
confers an increased susceptibility to the development
of lung cancer in smokers.
The presence of certain diseases of the lung,
notably chronic obstructive pulmonary disease
(COPD), is associated with an increased risk
(four to six times the risk of a nonsmoker)
for the development of lung cancer even after
the effects of concomitant cigarette smoking
Prior history of lung cancer
Survivors of lung cancer have a greater
risk than the general population of developing
a second lung cancer. Survivors of non-small
cell lung cancers (NSCLCs, see below) have an
additive risk of 1%-2% per year for developing
a second lung cancer. In survivors of small
cell lung cancers (SCLCs, see below), the risk
for development of second cancers approaches
6% per year.
Air pollution from vehicles, industry, and power
plants can raise the likelihood of developing
lung cancer in exposed individuals. Up to 1%
of lung cancer deaths are attributable to breathing
polluted air, and experts believe that prolonged
exposure to highly polluted air can carry a
risk for the development of lung cancer similar
to that of passive smoking.
Q. 4 : What are
the types of lung cancer?
Lung cancers, also known as
bronchogenic carcinomas (carcinoma is another
term for cancer), are broadly classified into
two types: small cell lung cancers (SCLC) and
non-small cell lung cancers (NSCLC). This classification
is based upon the microscopic appearance of the
tumor cells themselves. These two types of cancers
grow and spread in different ways and may have
different treatment options, so a distinction
between these two types is important.
SCLC comprise about 20% of lung cancers and
are the most aggressive and rapidly growing
of all lung cancers. SCLC are strongly related
to cigarette smoking, with only 1% of these
tumors occurring in nonsmokers. SCLC metastasize
rapidly to many sites within the body and are
most often discovered after they have spread
extensively. Referring to a specific cell appearance
often seen when examining samples of SCLC under
the microscope, these cancers are sometimes
called oat cell carcinomas.
NSCLC are the most common lung cancers, accounting
for about 80% of all lung cancers. NSCLC can
be divided into three main types that are named
based upon the type of cells found in the tumor:
* Adenocarcinomas are the
most commonly seen type of NSCLC in the U.S.
and comprise up to 50% of NSCLC . While adenocarcinomas
are associated with smoking like other lung
cancers, this type is observed as well in nonsmokers
who develop lung cancer. Most adenocarcinomas
arise in the outer, or peripheral, areas of
the lungs. Bronchioloalveolar carcinoma is a
subtype of adenocarcinoma that frequently develops
at multiple sites in the lungs and spreads along
the preexisting alveolar walls.
* Squamous cell carcinomas were formerly
more common than adenocarcinomas; at present,
they account for about 30% of NSCLC. Also known
as epidermoid carcinomas, squamous cell cancers
arise most frequently in the central chest area
in the bronchi.
* Large cell carcinomas, sometimes
referred to as undifferentiated carcinomas,
are the least common type of NSCLC.
* Mixtures of different types
of NSCLC are also seen.
Other types of cancers can
arise in the lung; these types are much less
common than NSCLC and SCLC and together comprise
only 5%-10% of lung cancers:
* Bronchial carcinoids account
for up to 5% of lung cancers. These tumors are
generally small (3-4 cm or less) when diagnosed
and occur most commonly in people under 40 years
of age. Unrelated to cigarette smoking, carcinoid
tumors can metastasize, and a small proportion
of these tumors secrete hormone-like substances
that may cause specific symptoms related to
the hormone being produced. Carcinoids generally
grow and spread more slowly than bronchogenic
cancers, and many are detected early enough
to be amenable to surgical resection.
* Cancers of supporting lung tissue such as
smooth muscle, blood vessels, or cells involved
in the immune response can rarely occur in the
Q. 5 : What are
the signs and symptoms of lung cancer?
Symptoms of lung cancer are
varied depending upon where and how widespread
the tumor is. Warning signs of lung cancer are
not always present or easy to identify. A person
with lung cancer may have the following kinds
* No symptoms: In up to 25%
of people who get lung cancer, the cancer is
first discovered on a routine chest X-ray or
CT scan as a solitary small mass sometimes called
a coin lesion, since on a two-dimensional X-ray
or CT scan, the round tumor looks like a coin.
These patients with small, single masses often
report no symptoms at the time the cancer is
* Symptoms related to the cancer: The
growth of the cancer and invasion of lung tissues
and surrounding tissue may interfere with breathing,
leading to symptoms such as cough, shortness
of breath, wheezing, chest pain, and coughing
up blood (hemoptysis). If the cancer has invaded
nerves, for example, it may cause shoulder pain
that travels down the outside of the arm (called
Pancoast's syndrome) or paralysis of the vocal
cords leading to hoarseness. Invasion of the
esophagus may lead to difficulty swallowing
(dysphagia). If a large airway is obstructed,
collapse of a portion of the lung may occur
and cause infections (abscesses, pneumonia)
in the obstructed area.
* Symptoms related to metastasis: Lung
cancer that has spread to the bones may produce
excruciating pain at the sites of bone involvement.
Cancer that has spread to the brain may cause
a number of neurologic symptoms that may include
blurred vision, headaches, seizures, or symptoms
of stroke such as weakness or loss of sensation
in parts of the body.
* Paraneoplastic symptoms:
Lung cancers frequently are accompanied by symptoms
that result from production of hormone-like
substances by the tumor cells. These paraneoplastic
syndromes occur most commonly with SCLC but
may be seen with any tumor type. A common paraneoplastic
syndrome associated with SCLC is the production
of a hormone called adrenocorticotrophic hormone
(ACTH) by the cancer cells, leading to oversecretion
of the hormone cortisol by the adrenal glands
(Cushing's syndrome). The most frequent paraneoplastic
syndrome seen with NSCLC is the production of
a substance similar to parathyroid hormone,
resulting in elevated levels of calcium in the
* Nonspecific symptoms: Nonspecific
symptoms seen with many cancers, including lung
cancers, include weight loss, weakness, and
fatigue. Psychological symptoms such as depression
and mood changes are also common.
Q. 6 : Does lung
cancer run in families?
: There are very few, if any,
inherited conditions that increase the risk of
lung cancer in non-smokers. However, not all of
the people who smoke get lung cancer and there
may be an inherited component which influences
whether or not smoking will cause lung cancer.