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Lung cancer
Dr Asheesh Mehta Internal Medicine Specialist November 09, 2017
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Lung cancer is the commonest cause of cancer related deaths in men and the second commonest, after breast cancer, in women. The tragedy about lung cancer is that most of these cancers and the resulting deaths are avoidable. Smoking is the biggest risk factor for lung cancer, long-term exposure to tobacco smoke being the cause in more than 80% cases. Creating awareness about lung cancer and the hazards of smoking thus continues to be very relevant. The observance of November as Lung Cancer Awareness Month makes it appropriate to highlight the main features of this often fatal disease. Of the estimated worldwide 8.8 million cancer deaths in 2015, lung cancer was responsibe for about 1.69 million deaths. It is also worth emphasizing that tobacco causes not only lung cancer but is also responsible for many other cancers and other major illnesses. According to the WHO tobacco is the cause in about 22% of cancer deaths.

Over the years survival rates of most types of cancers have improved substantially. The improvement has not been uniform for all types of cancers. For example, cure rates of breast cancer have improved greatly but those for other types of cancers such as oesophageal cancer, lung cancer and pancreatic cancer continue to be grim. The main reason for the poorer outcome in these cancers is the delay in diagnosis till the tumour is quite advanced and this in turn is due to late symptoms. It is true that symptoms are late in almost all cancers but this is particularly true for lung cancer. Even in cancers like breast cancer with much better survival rates, symptoms are quite late but increased awareness of the disease has led to much greater use of screening in the form of self examination, clinical examination and mammography with earlier detection and better outcome. Often, lung cancer is first detected when it has already spread to distant sites. Prognosis differs markedly depending on whether such spread has occurred. The 5 year survival of people with lung cancer detected when it has already spread beyond the lung is around 2% while it is above 40% when still localized to the lung. Lung cancer symptoms are late and often neglected till too late and this coupled with absence of widely adoptable screening methods causes delay in diagnosis and the poor prognosis. The lung cancer awareness campaign aims to bring into focus measures to reduce occurrence of lung cancer and to improve survival, should it occur, by measures such as early recognition of symptoms, early investigation of symptoms and most importantly, avoiding smoking.

A cancer is an uncontrolled growth of abnormal cells. There is normally a large turnover of cells in our body with new cells replacing worn out or damaged cells. The turnover of cells varies from organ to organ and also in different cell lines in a particular organ
A cancer is an uncontrolled growth of abnormal cells. There is normally a large turnover of cells in our body with new cells replacing worn out or damaged cells. The turnover of cells varies from organ to organ and also in different cell lines in a particular organ. In case any abnormal cell develops, this is detected by our immune system and destroyed. A cancer starts as a single abnormal cell that escapes destruction by the immune system. Many hundreds of generations of cancer cells originate from this single abnormal cell to cause a clinically apparent cancer. Cancer cells are not only abnormal in appearance under the microscope but exhibit uncontrolled and aggressive growth. They also tend to invade surrounding normal tissues and when carried along lymph or blood vessels form satellite lesions at distal sites which are called secondaries or metastases. Less common is the production of chemicals which mimic the action of biologically active substances such as hormones. These chemicals result in a variety of symptoms which can be very confusing as they mimic disease of hormonal or neurological  or gastrointestinal or other systems in the body.   Some types of lung cancer cause this type of syndrome which is known as nonmetastatic manifestation of a malignancy or as paraneoplastic syndrome.

Lung cancer may originate within the lung or may spread from another site such as the breast, stomach, colon, etc. Cancer originating in the lung is called primary lung cancer while that from a distant site is called secondary or metastatic lung cancer. When referring to lung cancer, it generally means primary lung cancer. There are two main types of lung cancer. Small cell lung cancer (SCLC) is also called oat cell lung cancer. The name derives from the size of cancer cells when viewed under a microscope. This occurs almost exclusively in smokers. It accounts for about 15 to 20% of all lung cancers. This cancer is usually an aggressive one. In most cases spread to distant sites has already occurred by the time it is diagnosed. Non-small cell lung cancer (NSCLC) is the other main type. It includes a number of subtypes including squamous cell cancer, adenocarcinoma and large cell lung cancer. Smoking is again the most important risk factor in NSCLC.

Smoking is the single most important risk factor for lung cancer. More than 80% of lung cancer is attributable to smoking. There is a substantial risk even with passive smoking. It is estimated that about a quarter of all lung cancers in nonsmokers are due to passive smoking. The risk from smoking increases with the duration and amount of smoking. After stopping smoking the risk reduces slowly but even 30 years after stopping smoking is double that in a nonsmoker. Asbestos is another important risk factor for lung cancer. The use of this material has been restricted to a very large extent in the last few decades. Smoking and asbestos exposure increase risk exponentially. Radon is an inert gas produced from decay of uranium. It is an important cause of cancer in uranium miners. Radon is also released due to decay of uranium in the earth’s crust and high concentrations may exist in buildings in vulnerable localities and may contribute to the risk of lung cancer. Other factors increasing risk for lung cancer include industrial substances such as arsenic, vinyl chloride, beryllium, some petrochemicals, etc. Air pollution too contributes to increased risk when level of cancer causing chemicals (carcinogens) is high in ambient air. Another factor is inheritance of specific genes increasing risk for lung cancer.

Persistent cough is a symptom of lung cancer. Cough is, however, a very common symptom and in most cases even persistent cough is due to another illness. Presence of blood in sputum, pain in the chest, breathlessness, etc may also suggest possible cancer but these are usually late symptoms. Systemic symptoms such as weight loss, loss of appetite and undue fatigue may occur as also symptoms from spread to a distant site such as the liver or brain or bone. A number of paraneoplastic syndromes suggesting disease of another organ of the body such as the nervous system, the endocrine system, the gastrointestinal system, etc may occasionally be the first or only manifestation of lung cancer. These symptoms suggestive of neuropathy, thyroid disease, etc often lead to a wild goose chase till direct symptoms of lung cancer finally appear.

Chest x-ray is the primary test in suspected lung cancer. Suspicious shadows or strong possibility of cancer in spite of normal x-ray warrant other imaging studies such as CT scan. Tissue obtained by various means including bronchoscopy or needle biopsy or even surgical biopsy is studied for the presence of cancer cells and also helps in determining the type of lung cancer. This also allows grading the cancer which gives an idea of the aggressiveness of the cancer. Staging is done to quantify size and spread of the cancer and tests include laboratory tests, CT and MRI of various organs, bone scans, etc.

Treatment depends on various factors including the type of lung cancer, staging, general condition of the patient and co-existence of other illnesses, age of the patient, etc. Surgery, radiation and chemotherapy have long been the mainstays of treatment of most types of cancers and this holds good for lung cancer too. It is ideal to surgically resect the tumour if at all possible. SCLC is usually a more aggressive type of cancer and most SCLC tumours have already spread beyond the lung at the time of diagnosis and surgery for the lung lesion, even when possible, has limited value. Even for NSCLC tumours it is common for distant spread to have already taken place before diagnosis. Stage I and II tumours are the ones where the tumour is still localized or has spread only locally and surgery to remove these tumours is strongly indicated. Surgical options range from removal of a wedge surrounding the tumour to complete removal of a lung depending on extent of the tumour and status of lung function. Radiotherapy and chemotherapy are important tools in treatment of lung cancer and attain even greater importance in patients in whom complete resection of the tumour is not achievable by surgery. A number of molecular-targeted therapies are also available. Cells of some lung cancers show specific mutations that make them vulnerable to drugs active against specific molecules. Such mutations are not identifiable in all lung cancers and also a number of different mutations of this type are possible. Hence, testing needs to be done to determine if the tumour is going to be susceptible to a particular type of treatment. Such testing as well as the drugs for this type of therapy are quite expensive. Further, results are quite variable from trial to trial. Most such therapy is still at a developmental stage and only a few drugs have been approved for general use. Such therapies, however, have given extremely encouraging results in selected cases.
 

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