Lung cancer: – It is also known as lung carcinoma, is a malignant lung tumor characterized by uncontrolled cell growth in tissues of the lung. This growth can spread beyond the lung by the process of metastasis into nearby tissue or other parts of the body.
Lung cancer is the uncontrolled abnormal cell growth and division in one or both of the lungs. Cigarette smoking causes most lung cancers when smoke gets in the lungs.
Tobacco smoke causes 90% of lung cancer. It also causes cancer in the larynx, head, neck, stomach, bladder, kidney, esophagus and pancreas. Tobacco smoke contains over fifty known carcinogens, including nitrosamines and polycyclic aromatic hydrocarbons.
Symptoms of lung cancer
These are the signs and symptoms of lung cancer:
Many of the symptoms of lung cancer are not specific, i.e. it may include poor appetite, weight loss, fever, and fatigue, etc. In many people, cancer already spread beyond the original site through metastasis. Symptoms that suggest the presence of metastatic disease include weight loss, bone pain or limb weakness.
(i) Respiratory symptoms: coughing, coughing up blood, wheezing, or shortness of breath
(ii) Symptoms due to the cancer mass pressing on adjacent structures: chest pain, bone pain, superior vena cava obstruction, or difficulty swallowing
(iii) Systemic symptoms: weight loss, weakness, fever, or clubbing of the fingernails
(iv) If cancer grows in the airways or respiratory tract, it may obstruct the flow of air and causing breathing difficulties.
Common sites of spread include the brain, bone, adrenal glands, opposite lung, liver, pericardium, and kidneys. Very few people with lung cancer do not have symptoms at diagnosis; because these cancers are incidentally found on routine chest radiography.
Causes of lung cancer
Lung Cancer develops after genetic damage to DNA. This change affects the cell’s normal functions, including cell proliferation, controlled cell division, and cell death and DNA repair. The risk of cancer increases.
These causes are responsible for lung cancer:
Tobacco smoking is the main cause of lung cancer. It causes almost 85 – 90% of lung cancer. Cigarette smoke contains at least 73 known carcinogens, including benzopyrene, NNK, 1,3-butadiene, and a radioactive isotope of polonium.
(i) Passive smoking: It is the inhalation of smoke from another’s smoking. This is a cause of lung cancer in nonsmokers. A passive smoker can be defined as someone either living or working with a smoker.
Passive smoking is more dangerous than direct smoke or active smoking.
(ii) Cannabis smoking: It is the inhalation of smoke or vapors which is released by heating the flowers, leaves, or extracts of cannabis and releasing the main psychoactive chemical, tetrahydrocannabinol (THC), which is absorbed into the bloodstream via the lungs.
Many outdoor air pollutants, especially chemicals released from the burning of fossil fuels, increase the risk of lung cancer. Micro-particulates and sulfate aerosols, which may be released in traffic exhaust fumes, are associated with a slightly increased risk. Nitrogen dioxide also increases the risk of lung cancer.
Much indoor air pollution also increases the risk of lung cancer, these include the burning of wood, charcoal, dung, or crop residue for cooking and heating.
About 8% of lung cancer is caused by abnormal inherited factors. In relatives of people that are diagnosed with lung cancer, the risk is doubled, likely due to a combination of genes. Polymorphisms on chromosomes 5, 6, and 15 are known to affect the risk of lung cancer.
Some other substances, occupations, and environmental exposures have been recognized as the cause of lung cancer.
(i) Some metals like cadmium, chromium, beryllium, arsenic, etc.
(ii) Some products of combustion like incomplete combustion, coal burning, coal-tar pitch, coke production, diesel engine exhaust, etc.
(iii) Ionizing radiation like X-ray and gamma-ray.
(iv) Some toxic gases like Dimethyl ether, Bis-(chloromethyl) ether, sulfur mustard (mustard gas), etc.
Diagnosis of lung cancer
Performing a chest radiograph is one of the first investigative steps if a person reports symptoms that may be suggestive of lung cancer. CT imaging is typically used to provide more information about the type and extent of disease. Bronchoscopic or CT-guided biopsy is often used to sample the tumor for histopathology.
Lung cancer often appears as a solitary pulmonary nodule on a chest radiograph. However, the differential diagnosis is wide. Many other diseases can also give this appearance, including metastatic cancer, hamartomas, and infectious granulomas caused by tuberculosis, histoplasmosis or coccidioidomycosis.
The definitive diagnosis of lung cancer is based on the histological examination of the suspicious tissue in the context of the clinical and radiological features.
CT imaging should not be used for longer or more frequently than indicated, as the extended surveillance exposes people to increased radiation and is costly.
Lung cancer can also be an incidental finding, as a solitary pulmonary nodule on a chest radiograph or CT scan done for an unrelated reason.
Types of lung cancer
Lung cancers are classified according to histological type:
Lung cancers are carcinomas – malignancies that arise from epithelial cells. Lung carcinomas are categorized by the size and appearance of the malignant cells seen by a histopathologist under a microscope.
On the basis of therapeutic purposes, two broad classes are distinguished:
1. Non-small-cell lung carcinoma
2. small-cell lung carcinoma
1. Non-small-cell lung carcinoma:
There are three subtypes of Non-small-cell lung carcinoma are adenocarcinoma, squamous-cell carcinoma, and large-cell carcinoma.
(a) Adenocarcinoma: It is the most common type of lung cancer, and like other forms of lung cancer, it is characterized by distinct cellular and molecular features.
Although most cases of adenocarcinoma are associated with smoking.
(b) Squamous-cell carcinoma: It is more common in men than in women. It is closely correlated with a history of tobacco smoking. They typically occur close to large airways. A hollow cavity and associated cell death are commonly found at the center of the tumor.
(c) Large-cell carcinoma: It is a heterogeneous group of undifferentiated malignant neoplasms that lack the cytologic and architectural features of small cell carcinoma and glandular or squamous differentiation.
These are “Large-cell carcinoma” named because the cancer cells are large, with excess cytoplasm, large nuclei, and conspicuous nucleoli.
2. small-cell lung carcinoma:
In small-cell lung carcinoma, the cells contain dense neurosecretory granules (vesicles containing neuroendocrine hormones), which give this tumor an endocrine or paraneoplastic syndrome association.
Most cases arise in the larger airways like primary and secondary bronchi.
Prevention of lung cancer
These are some ways to prevent the development of lung cancer:
(i) Smoking ban: Eliminating tobacco smoking is a primary goal in the prevention of lung cancer, and smoking cessation is an important preventive tool in this process.
(ii) Screening: Cancer screening uses medical tests to detect disease in large groups of people who have no symptoms. For individuals with high risk of developing lung cancer, computed tomography (CT) screening can detect cancer and give a person options to respond to it in a way that prolongs life.
CT screening is associated with a high rate of falsely positive tests which may result in unneeded treatment. For each true positive scan, there are about 19 falsely positives scans.