Cancer has emerged as the most dreaded ailment in
recent times and is one of the major causative factors for
mortality worldover. In spite of developments and continuous
research for determining the causative factor, efficient
treatment strategies and classification of cancer, the death toll still remains
high. There are more than 200 types of cancers which have been known to
affect more than 60 different sites in the human body. Few of these like cancer
of the breast cancer, lung cancer, colon, colorectal, blood, etc.
have been documented to have a higher prevalence. Lung cancer is the third most prevalent
type in men and women and the most common cause of cancer deaths worldwide.
Let us understand lung cancer in more detail including its types, symptoms, diagnosis and
current treatment modalities available.
Lung cancer Overview
Cancer or neoplasm is defined as an uncontrolled cellular growth. They can be broadly
classified depending on the site of growth as lung cancer, oral cancer breast cancer, cervical
cancer, etc. They can also be classified on the basis of cell of origin as squamous cell carcinoma
or adenocarcinoma. There are two types of lung cancers or carcinomas (cancer that begins in the
skin or in any tissue that line or cover the internal organs) viz. Small cell lung cancer and non-
small cell lung cancer. If not treated immediately these cancer cells can metastasise i.e. migrate
to the nearby tissues and start multiplying
Small cell lung cancer (SCLC) About 10-15% of the lung cancers belong to this type and it
usually occurs in or around the bronchi, hence is centrally located. It is an aggressive tumour
that can spread to other parts of the body. These cells look small and have oval nuclei with
characteristic salt and pepper chromatin, when observed under microscope. Small cell lung
cancer may be solely composed of the typical small neuroendocrine cells or may be combined
with some other non-small cell component (combined small cell cancer).
Non-small cell lung cancer (NSCLC)
These are more common than SCLC and account for
about 85-95% of all lung cancers. These are further subclassified on the basis of predominant
cell type in the tumour tissue, identified by microscopic examination. There are three types of
non-small cell lung cancer viz. squamous cell carcinoma, large cell carcinoma and adenocarcinoma.
Squamous cell carcinoma
About 25-30% of NSCLC are squamous cell carcinomas. This type of
cancer originates due to metaplasia in the epithelial lining of the airways and is connected to the
history of Smoking.
Adenocarcinoma About 40% of NSCLC are adenocarcinomas which begin in the mucous secreting
cells lining the air sacs
and hence are usually peripherally located. Men seem
to be more affected than women and the incidence is
higher among the younger age groups. This type of
cancer grows very slowly than any other type. They are
more commonly found in non-smokers and are the most
which ultimately leads to the development of cancer.
common subtype of primary tumours in women.
Large cell carcinoma
This subtype forms 10-15% of all primary tumours in
lung and it can occur in any part of the organ. It has the
ability to grow at a faster rate and hence it may become
difficult to treat. It is an aggressive, undifferentiated
tumour which has lost all resemblance to the cell of
origin.
Causes / risk factors for lung cancer
Smoking is considered to be one of the most important causes of lung cancer.
It is considered to be the most important etiological factor for the development
of squamous cell carcinoma. However, because of changes in smoking patterns
due to awareness created by electronic media, adenocarcinoma has replaced
squamous cell carcinoma as the most common primary lung tumour in recent
years. To understand further about the pathogenesis of lung cancer, let's
understand some of the risk factors for development of lung cancer
Smoking is the 1st cause of cancer
Cigarette smoke is composed of many hazardous substances which have the ability to bind to
DNA of the cells, thereby hampering their normal functioning ultimately leading to cancer. The
four main causative agents include benzene, polonium-210 (absorbed in tobacco leaves from
soil), benzo-(a)-Pyrene and nitrosamines. Apart from these, cigarette smoke also
contains certain heavy metals like chromium which
enhances the binding ability of benzo-(a)-pyrene,
arsenic and nickel interfere in the DNA repair pathway
on immune system which encourages the growth of
cancer cells. It takes many years or even decades of
smoking to cause cancer as the body's immune system
tries its best to cope up with the effects of toxic chemicals
entering your body each time you smoke . But continuous
smoking for many years may eventually lead to developments
of lung cancer
Passive smokers
Researchers have shown that passive smokers also have 24% increased chances of
developing lung cancer as compared to non-smokers.
Asbestos fibers
Asbestos fibers are silicate fibers which have the ability of persisting in the lung tissue for
lifetime and generally enter through inhalation. Asbestos is generally used in thermal and
acoustic insulation material and exposure is associated mainly with occupational hazard.
BANI (Ban Asbestos Network of India) is a network which includes a group of scientists,
public health researchers, doctors, trade union activists and many more who have succeeded
in drawing attention of people towards the hazardous affects of asbestos on the environment
as well as human health.
Others
Apart from the above mentioned causes or risk factors, radon gas (that is released when
uranium decays) and air pollution (due to carcinogenic fumes released from vehicles) also
increase the chances of lung cancer.
Symptoms of lung cancer
- Persistent cough for 2-3 weeks
- Blood in sputum
- Persistent chest infection
- Persistent breathlessness
- Pain when breathing or coughing
- Shortness of breath
Diagnosis of lung cancer
On visit to a clinic with the above symptoms, a detailed
chest examination is done by the physician to identify
the site of the lesion and detect the presence of
concomitant pleural effusion. Blood tests is also suggested if
infection in the chest is suspected as a differential diagnosis.
- X-ray is done as a preliminary test followed by CT scan
(Computerised Tomography) for confirmation.
- In case of a positive CT scan, a biopsy is also done using a bronchoscope.
Bronchoscopy is a technique which involves use of a tube inserted in the
lungs either through mouth or nose and the tumour cells or fluid is taken
for further examination.
- In addition to the above tests, tumour markers like CEA, CYFRA 21-1, NSE can also
be used for diagnosis and follow-up of lung cancers.
PET-CT (Positron Emission Tomography) scan is done for initial staging in patients
with NSCLC and selected patients with SCLC or for characterisation of an indeterminate
pulmonary nodule which is at least 8-10 mm in diameter. In PET-CT scan, a radioactive
material is injected in the body which binds to the cancer cells and helps to determine a
detailed information on the type of tumour i.e benign or malignant, stage of the cancer,
etc.
Treatment
There are different types of treatment modalities available for lung cancer which include
surgery, radiation, chemotherapy, etc. The type of treatment depends upon the stage of
cancer.
Surgery
It is used in the initial stages of the cancer when the tumour mass is restricted to a particular
lobe of lung and has not spread to neighbouring regions or to distant sites. The entire tumour
is surgically removed from the site along with the surrounding lymph nodes. There are different
types of surgeries
- Lobectomy: Lungs are composed of 3 lobes on the right side and 2 on the left. In this surgery,
the entire tumour containing lobe is removed.
- Wedge resection: If removal of lobe is not possible then the tumour surrounded by the margin
of normal lung is removed.
- Segmentectomy: Lung is further subdivided into broncho pulmonary segments based on the
branching of bronchus and the vascular supply. Segmentectomy involves removal of the involved
segment of the lung. However, this minimal resection surgery can only be done if the tumour size
is very small.
- Pneumonectomy: The entire lung is removed wherein the cancer has developed.
Radiation therapy
Radiation therapy is a highly targeted and effective way of cancer treatment. The commonly
used method is external beam radiation therapy where radiation is given from outside of the
body. This therapy is also effective in the initial stages. Sometimes CT scan is used to identify
the exact location of cancer cells in order to minimise damage to the normal cells.
Chemotherapy
Chemotherapy is a treatment mode involving use of drugs. Medication is given either
intravenously or orally depending on the stage of cancer. The only draw back of chemotherapy
is, it has many side effects like hairloss, fever, bone marrow suppression, etc.
Targeted therapy
Proteins or specific genes of the DNA of cancerous cells are targeted in this therapy.
Nanotechnology is playing a key role nowadays wherein the anti-cancer drugs are
loaded in nano particles and injected into the body. These bind to the targeted site
and release the drug, thus causing targeted destruction of cancerous cells.
Prognosis and prevention of lung cancer
Whenever a person is diagnosed with lung cancer, the 1" question that comes in mind is
prognosis of cancer and whether its curable. However, prognosis depends upon the stage
of cancer at the time of presentation. If lung cancer is diagnosed in the early stage then the
chances of survival increases. And with the availability and use of multimodality therapies
as explained above, the chances of survival may further increase. But if the cancer is diagnosed
at a later stage, when it has metastasised to other part of the body, then the 5 year survival
rate drops down to just 4%.
As prevention is always better than cure, it is always better to
know the risk factors that can lead to lung cancer and take preventive steps which include:
Stop smoking
Ban smoking in public spaces to reduce exposure to second hand smoke.
Healthy diet (low fat, high fiber, fresh fruits, vegetables, whole grain)
Exercise: Daily moderate-intensity aerobic activity reduces lung cancer risk.
Finally, the most important, try to keep your environment free from pollution.
