Lung cancer originates from the tissues of the lung, usually from cells lining the air passages. The two main types are small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC). It is the second most common cancer in men and the fifth most common cancer in both men and women together.
The risk of getting lung cancer for smoker to non-smoker is 20:1 as per various studies.
The most common kind of lung cancer, accounting for nearly 90% of diagnoses. NSCLC’s can be further split into three types: adenocarcinoma, squamous cell carcinoma and large cell carcinoma.These subtypes, which start from different types of lung cells are grouped together as NSCLC because their treatment and prognosis are often similar.
Adenocarcinoma: Adenocarcinomas start in the cells that would normally secrete substances such as mucus.This type of lung cancer occurs mainly in current or former smokers, but it is also the most common type of lung cancer seen in non-smokers. It is more common in women than in men, and it is more likely to occur in younger people than other types of lung cancer.Adenocarcinoma is usually found in the outer parts of the lung and is more likely to be found before it has spread.
Squamous cell carcinoma: Squamous cell carcinomas start in squamous cells, which are flat cells that line the inside of the airways in the lungs. They are often linked to a history of smoking and tend to be found in the central part of the lungs, near a main airway (bronchus).
Large cell (undifferentiated) carcinoma: Large cell carcinoma can appear in any part of the lung. It tends to grow and spread quickly, which can make it harder to treat. A subtype of large cell carcinoma, known as large cell neuroendocrine carcinoma, is a fast-growing cancer that is very similar to small cell lung cancer.
About 10% to 15% of all lung cancers are SCLC and it is sometimes called oat cell cancer.
This type of lung cancer tends to grow and spread faster than NSCLC. About 70% of people with SCLC will have cancer that has already spread at the time they are diagnosed. Since this cancer grows quickly, it tends to respond well to chemotherapy and radiation therapy. Unfortunately, for most people, the cancer will return at some point.
If your doctor suspects you might have lung cancer, he will ask you about the presence of risk factors like smoking, your occupation, etc. He will also examine you for signs of lung cancer and other health problems.
Depending upon the findings, the doctor might advise certain tests.
Chest X-ray: This is usually the first test your doctor will get done to look for a mass in the lungs. If something suspicious is seen in the X-ray, further tests will be ordered.
Computed tomography (CT) scan: A CT (or CAT) scan is more likely to show lung masses than X-ray. CT scans can also provide information about the size, shape and position of lung tumors and help find spread of the cancer to lymph nodes or other organs.
CT-guided needle biopsy: If a suspicious mass is seen in the lung during CT scan, your doctor may perform a guided biopsy to take some tissue for diagnosis.
Magnetic resonance imaging (MRI) scan: MRI scans are most often used to look for spread of lung cancer to brain and spinal cord to help in staging of the cancer. Unlike CT scans, MRI uses radio waves and strong magnets and there is no exposure to radiation.
Positron emission tomography (PET) scan: A PET scan can be used to see if the cancer has spread to lymph nodes or other areas. This determines whether surgery can be done or not. PET scan is also useful if your doctor thinks that your lung cancer has spread but does not know where.
Sputum Cytology: A sample of sputum (mucus that is coughed up from lungs) is viewed under a microscope to look for cancer cells. For this, the best method is to submit early morning sputum samples obtained after a deep cough for 3 days in a row.
Thoracocentesis: This procedure is performed if there is a buildup of fluid around the lungs (pleural effusion), which can cause difficulty in breathing. A hollow needle is inserted between the ribs to drain the fluid and check for tumor cells in the fluid (effusion cytology)
Needle biopsy: This involves the insertion of a hollow needle into the mass to get a small sample for testing. It can be done by fine needle aspiration biopsy (FNAB), where a very fine needle with syringe is used to withdraw or aspirate cells and fragments from the mass; or core biopsy, in which a larger needle is used to remove small cylinders or cores of tissue. This procedure is performed under local anesthesia and radiologist’s guidance. A possible complication of the biopsy procedure is air leak from the lung into the space between lung and chest wall (pneumothorax ). When large, it may lead to collapse of a part of the lung and trouble in breathing. This is usually self limiting and gets better without any treatment.
Core biopsy: A larger needle is used to remove one or more small cores of tissue. Samples from core biopsies are often preferred because they are larger than FNA biopsies.
Immunohistochemistry (IHC) Testing: Tissue sample is taken from the cancer site and sent to pathology lab to see if the programmed cell death ligand (PD-L1) is expressed in their cancer. Your doctor will recommend to test the biopsy sample to know if your cancer will respond to Immunotherapy.
Genomics & Transcriptomics : Tests that can identify DNA-& RNA based changes (point mutations, gene amplification, fusion, deletion, insertion, or nucleotide polymorphisms) leading to abnormality at the gene level and requires personalised medicine approach. Tests can range from single gene test, panel of genes,whole exome sequencing, RNA sequencing etc.
These tests can be done on tissue taken during a biopsy or surgery for lung cancer. If the biopsy sample is too small and all the tests cannot be done, the testing may also be done on blood that is taken from a vein just like a regular blood draw. This blood contains the DNA from dead tumor cells found in the bloodstream of people with advanced lung cancer. Obtaining the tumor DNA through a blood draw is sometimes called a "liquid biopsy" and can have advantages over a standard needle biopsy, which can carry risks like a pneumothorax (lung collapse) and shortness of breath.
Your doctor may look for specific gene changes in the cancer cells that could mean certain targeted drugs might help treat the cancer. For example:
EGFR is a protein that appears in high amounts on the surface of 10% to 20% of NSCLC cells and helps them grow. Some drugs that target EGFR can be used to treat NSCLC with changes in the EGFR gene, which are more common in certain groups, such as non-smokers, women, and Asians. But these drugs don’t seem to be as helpful in patients whose cancer cells have changes in the KRAS gene. Doctors now test NSCLC cells for changes in genes such as EGFR and KRAS to determine if these newer treatments are likely to be helpful.
About 5% of NSCLCs have a change in the ALK gene. This change is most often seen in non-smokers (or light smokers) who have the adenocarcinoma subtype of NSCLC. Doctors may test cancers for changes in the ALK gene to see if drugs that target this change may help them.
About 1% to 2% of NSCLCs have a rearrangement in the ROS1 gene, which might make the tumor respond to certain targeted drugs.
A small percentage of NSCLCs have changes in the RET gene. Certain drugs that target cells with RET gene changes might be options for treating these tumors.
About 5% of NSCLCs have changes in the BRAF gene. Certain drugs that target cells with BRAF gene changes might be an option for treating these tumors.
A small percentage of NSCLCs have certain changes in the MET gene that make them more likely to respond to some targeted drugs.
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