There are two main types of lung cancer: small cell lung cancer and non-small cell lung cancer.
Lung cancer can also be classified as primary and secondary lung cancers. Primary lung cancer starts inside the lungs, as opposed to secondary lung cancer, which spreads from other body areas into the lungs.
Depending on specific characteristics of the malignancy, primary and secondary lung cancers are divided into many kinds.
The two main primary types of lung cancer:
Lung cancers are generally classified as:
- Small cell lung cancer.
- Non-small cell lung cancer.
Small cell lung cancer is a rapidly spreading cancer of neuroendocrine origin. It has two different subtypes:
- Oat cell cancer
- combined small cell lung cancer
Non-small cell lung cancer has three main subtypes [Ref]:
- Squamous cell carcinoma
- Large cell carcinoma
There are other rare subtypes of non-small cell lung cancers as well.
Small cell lung cancer (SCLC)
Small cell lung cancer is a type of malignant lung cancer that spreads rapidly but is not common. Typically it grows in the tissues of the lung.
It is also known as Oat Cell cancer, due to the appearance of oval-shaped cells like the oat grains. It is one of the most common cancers that returns after treatment.
Around 15-20% of lung cancers are of this type. So it means that about 150-200 out of 1000 lung cancer patients are with SCLC. Sometimes cancer spreads in the neuroendocrine cells of the lungs. That is why they are also classified as neuroendocrine tumors.
Causes of small cell lung cancer:
- Smoking has been regarded as the most common cause of lung cancer
- Passive smoking is also dangerous and can cause cancer.
- Radiations in the environment.
- Hereditary lung cancer.
- Viruses like the Human immunodeficiency virus (HIV) can also cause lung cancer of this type.
- Age can be a key factor in the occurrence of lung cancer.
- Industrial compounds like asbestos, tar, nickel, lead, etc can cause cancer.
The onset of this type of cancer can cause different sign and symptoms which includes the following:
- Chest pain and tightness are the common symptoms of all lung cancer.
- Long-standing cough.
- Blood in coughing is also known as hemoptysis.
- Trouble in respiration along with wheezing sound.
- Facial edema.
- Loss of appetite is also seen.
- Weight loss and engorged neck veins.
Prevalence of SCLC:
SCLC makes for roughly 13% of all lung malignancies in general. [Ref]
About 10%–15% of patients with lung cancer have SCLC. In the US, between 30,000 and 35,000 new cases of SCLC are diagnosed every year. [Ref]
How to diagnose small cell lung cancer?
The typical method which is used to diagnose cancer is through chest X-ray. If someone is having a problem, scars at different locations in the lung appear.
Apart from this, some other techniques are used by the doctor to confirm the findings from the X-ray. These are as follows:
- CT scan (computed tomography).
- Bronchoscopy to check the airways and lungs.
- Checking for cancer cells in the sputum or mucus coming from the lungs is done using sputum cytology.
- Lung biopsy
Stages of small cell lung cancer:
Depending on the extent of the malignancy, small cell lung cancer has two stages. These are :
- Limited cancer is one that is limited to a certain fixed location either within the single lung or in the lymph nodes of that lung.
- Extensive cancer is the one in which cancer has spread to both the lungs and lymph nodes and can be metastasized in nearby or distant locations like in the bone or even in the brain.
Treatment of small cell lung cancer (SCLC):
There are different approaches to treating small cell lung cancer. Though it is treatable but not curable.
We use these approaches according to the patient’s health status, patient’s age, and cancer stages. Some of these are given below:
- Radiation therapy is the basic form of treatment in the case of cancers in which X-rays of fixed and bearable wavelengths are given to the patients, which results in the killing of cancerous cells in the body.
- Chemotherapy is considered one of the best remedies for cancers. Though it is painful and has side effects, it helps to kill cancerous cells rapidly and effectively.
- Immunotherapy is also the choice of treatment to treat cancer. In this, the drugs act by activating the immune system of the patient.
- It is helpful in the initial stages of cancer but after some time, the immune system gets weakened and the immunity is compromised.
- Immune checkpoints are there in the body and the drug inhibits these points to cause extensive immune activity in the body.
- Surgery is not common but is done in some cases. If the tumor is restricted to a small area like a lump, it can be resected by performing surgery but if the cancer is metastasized, nothing can stop it from spreading to different locations and death pursue after some time.
Non-small cell lung cancer
Being the most common type of all sorts of lung cancer, it comprises approximately 85% or three-fourths of all cases of lung cancer.
Even though it spreads much slower than SCLC but it still spreads to extended areas by e time it is diagnosed. Non-small cell lung cancer comes in three primary subtypes, each of which is discussed individually.
Type of non-small cell lung cancer:
- Squamous cell carcinoma.
- Large cell carcinoma.
Squamous cell carcinoma:
- It is also known as epidermoid carcinoma. It spreads rapidly in the lungs. Typically it is the cancer of squamous cells that lines the internal aspects of the lungs.
- Squamous cells are flat in appearance and these cells are mostly destroyed by smoking.
- Adenocarcinoma of the lung is the most common form of lung cancer in the United States and it is the leading cause of death by cancer.
- Adenocarcinoma begins in the glandular tissues anywhere in the body. It is metastasized slowly in the body.
- Normally it is found in the peripheral regions of the lungs. In the beginning, it does not appear usually. So it is diagnosed when cancer has acquired a greater portion of the organ.
Large cell carcinoma:
- This type of NSCLC spreads quickly, making it more lethal and difficult to treat. It is also known as undifferentiated carcinoma because the cells in this cancer are not well defined. It can spread anywhere in the lungs.
Causes of non-small cell lung cancer:
There are different causes of such cancers, out of which some are listed below:
- Again, smoking is the main factor in developing this cancer. NSCLC may develop as a result of past smoking.
- Exposure to some substances like asbestos, lead, etc can result in cancer if its exposure is frequent.
- Radioactive gases like radon are also carcinogenic in nature.
- Chronic obstructive pulmonary disease can lead to cancer after some time.
- Pulmonary fibrosis.
- Viral infections of HIV or AIDS can be the source of cancer.
- Radiations in the environment can destroy the tumor suppressor genes.
Symptoms of non-small cell lung cancer:
The symptoms of lung cancer may be subtle and missed. Depending on the stage of lung cancer, symptoms can be variable. These are given below:
- Shortness of breath and coughing are the prompt symptoms of NSCLC. These symptoms usually remain till the death of the patient.
- Chest discomfort.
- Wheezing with trouble breathing.
- Hemoptysis (coughing up blood)
- Change in voice.
- Dysphagia (Difficulty swallowing)
- Weight loss is seen due to loss of appetite.
- Edema and swelling of neck veins are also reported.
How to diagnose non-small cell lung cancer?
Different methods are used to detect cancer. Some are described below:
- A blood or urine sample can be helpful.
- Chest X-rays.
- CT scans or PET.
- Biopsy of the lung tissues.
- Sputum cytology.
- Thoracoscopy, in which the thoracic region is examined with the help of a camera or video.
Staging of non-small cell lung cancer:
Staging is an important part of lung cancer treatment. The intensity, duration, and modality of treatment are decided by the stage of cancer.
- It refers to the abnormal lump over the top of lung layers.
- Stage 1 is defined as cancer that spreads within the lungs only.
- Stage II non-small cell lung cancer is when it spreads only to some lymph nodes.
- Stage III predicts that the tumor has spread into other nearby tissues.
IV and final stage:
- It describes that the tumor is dislodged from the point of origin.
Cancer is spread via two sources, either it can be the blood or the lymphatic system.
Treatment of non-small cell lung cancer:
Almost the strategies to treat the cancer are same which are described above which include:
- Surgery in which lobectomy or lung resection can be done to stop the growth of a tumor.
- Radiofrequency ablation is common when surgery is not an option for the patient. Tumor cells are destroyed by heating through radio waves of high energy.
- Radiotherapy uses X-rays to kill the cancerous cells in the body.
- Chemotherapy is typically done by giving drugs to the patient. It is preferred over radiotherapy because it only kills the cells that are cancerous while radiotherapy kills the normal cells as well.
- Targeted drugs like monoclonal antibodies and tyrosine kinase inhibitors are used as well.
- Immunotherapy is also a choice of treatment by doctors.
Prevalence of non-small cell lung cancer:
The second most prevalent cancer diagnosed globally is lung cancer. In the United States, NSCLC accounts for 82% of all lung cancer diagnoses, making it the most prevalent kind of disease. [Ref]
Differences between the two types of lung cancer: SCLC and NSCLC
- In SCLC, the cancerous cells are small when seen under a microscope while in NSCLC the cells are larger in size.
- SCLC grows more rapidly as compared to NSCLC.
- NSCLC is diagnosed normally after it is metastasized to different tissues of the body while SCLC is diagnosed earlier than NSCLC.
- SCLC is easy to treat while NSCLC is difficult to treat.