Lung cancer is the second commonest cancer. All cancers taken together cause about 9.6 million deaths annually with lung cancer alone accounting for 1.76 million deaths. The dubious distinction of being by far the leading cause of cancer related deaths in both men and women is reason enough to create greater awareness of the disease. Lung cancer is responsible for more deaths than cancers of the breast, prostate and colon combined. When one considers that the majority of lung cancer cases are preventable, this is all the more relevant. November is observed as Lung Cancer Awareness Month with a large number of health organisations and volunteer organisations participating.
A cancer or carcinoma is unrestrained and unregulated growth of abnormal cells anywhere in our body. Uncontrolled growth of cancer cells is at the cost of normal cells. Cancer cells cause symptoms because of local damage at the area of origin and these cells also spread to contiguous organs and by the blood stream and lymphatics to distant sites. Cancer lesions in locations distant from the site of origin are called secondaries or metastases. As far as lung cancer is concerned there are two main types, depending on the type of cells making up the cancer. The commoner one is called non-small cell lung cancer (NSCLC) and is the type in about 85% of lung cancer cases. The other one is small cell lung cancer (SCLC). The lung is also a preferential site for secondary cancer from many distant sites such as the breast, colon, stomach, etc. However, metastatic cancers in the lung are considered as part of the original cancer rather than as a true lung cancer. NSCLC is further classiied into different types depending on the appearance of the cells when inspected under a microscope after appropriate staining. Types include adenocarcinoma, squamous cell carcinoma and large cell carcinoma. Adenocarcinoma is the commoner type comprising about 40% of all lung cancer cases while squamous cell carcinoma makes up about 30% of cases. SCLC, although making up only about 15% of cases, is noted for its aggressive behavior with rapid distant spread and generally much worse prognosis. Other types of cancers in the lung such as carcinoid tumour are relatively rare.
The single most important cause of lung cancer is smoking. About 90% of lung cancers are attributed to smoking, whether active or passive. Risk of lung cancer from smoking rises with the quantum as well as duration. Cigarette smoking has the highest risk but other modes of smoking such as cigar and pipe smoking too impart a substantial risk. In fact, second hand smoke too is dangerous. Although the increased risk of lung cancer starts reducing on quitting smoking it takes about 15 years for the risk to be near what it is for a nonsmoker. Air pollution is another important risk factor acting in a somewhat similar manner to smoking by inhalation of noxious cancer causing chemicals. Among other causes of lung cancer are exposure to industrial products or minerals with asbestos being the most well established association. Smoking in a person with asbestos disease of the lung increases the risk for lung cancer exponentially. Asbestos has been replaced with safer materials in most applications and workers in this industry are also better protected and monitored much more closely than used to be the case in earlier times. Exposure to silicon dust too may enhance risk for lung cancer. Exposure to radon gas is another important contributory factor. Radon is an inert gas generated as a decay product of uranium. Radon itself decays rapidly with emission of harmful ionizing radiations. Radon exposure generally occurs due to inherent radioactivity in the soil in a particular area. Since the gas is odourless and colourless we cannot detect its presence except with speciic equipment. The US Environmental Protection Agency estimates that about 1 in 15 homes in the USA contains dangerous levels of radon. Radon contributes to about 10% of all lung cancer causation.
Symptoms typically arise late in cases of lung cancer. In fact, in quite a few individuals with lung cancer there are no symptoms at the time of diagnosis, the tumour having been detected during incidental or screening x-ray of the chest. Symptoms may include persistent cough, breathlessness and chest pain. Any new onset cough or worsening of an existing cough which persists more than a week or two, especially in smokers, merits attention. Should the cough be associated with bloody sputum it has even more ominous signiicance. While most such coughs turn out to be due to more innocuous problems such as pharyngitis or bronchitis, a persistent cough needs investigation to rule out lung cancer. Chest pain may be complained of during coughing or apart from the cough. Breathlessness on exertion or even at rest may be present and may signify problems like collection of luid in the pleural cavity around the lung or the cancer obstructing low of air into part of the lung. Other complaints include unexplained loss of appetite and weight and excessive fatigue. Spread to distant sites may be the irst intimation of lung cancer. Symptoms in this case depend on the site of spread and the severity of lesion. The bones are often the site of secondaries from lung cancer with common sites being the spine, the thigh bones, pelvis and ribs and may present with bone pains at these sites. The liver and brain are other common sites for lung cancer to spread. In some people with lung cancer symptoms attributable to what are called paraneoplastic syndrome occur. Unusual symptoms not due to the mass effect of the tumour or to distant spread occur. For instance, serum calcium levels may be elevated or thyroid hormone levels may be high or there may be symptoms suggestive of nerve degeneration. Some of these syndromes are due to aberrant production of chemicals by the tumour while in others the mechanism of symptoms is not clear. The underlying cause for these atypical symptoms is easily overlooked by the unwary physician till late.
For diagnosis of lung cancer, x-ray chest is quite helpful as a screening tool. CT scan and MRI are more sensitive imaging tests. Bronchoscopy involves passage of a thin endoscope into the larger air passages through the nose or the mouth and inspecting the image on a video monitor or through the eyepiece. Tissue samples can also be collected for cytological examination for cancer. The sputum can also be evaluated for cancer cells but the yield is less satisfactory. Biopsy to obtain tissue for microscopic examination can also be carried out by a needle introduced through the skin or by special tests such as mediastinoscopy or even by surgery; the selection of route depends on the location and other characteristics of the lesion as seen on x-ray and other imaging tests. Conirmation of cancer diagnosis by cytology or histopathology is of obvious importance in planning treatment. Investigations are also required to detect if the cancer remains localized to the lung or has spread to contiguous areas or distant sites.
Treatment depends on the stage and whether it is of NSCLC or SCLC type. Stage 1 is a small cancer that is localized to the site of origin while stage 4 cancer refers to one that has spread to distant sites. The notoriously poor prognosis of lung cancer is largely due to most cancers being detected late in the course of the disease. The 5 year survival for a stage 4 lung cancer is less than 5% while those with disease without distant spread have about a 50% survival rate. Surgery to remove resectable cancers along with chemotherapy and radiation to prevent recurrence are the standard conventional modes of lung cancer therapy. If surgery is not possible chemotherapy and / or radiotherapy may offer palliation. Surgery is rarely possible in SCLC because rapid spread of this type of cancer means that metastases are already present in most cases at the time of diagnosis. Targeted therapy is another option in selected cases. These are agents that are effective when speciic mutations are present in cancer cells. Testing for these mutations is done at initial diagnosis. A very large number of different molecules have been used in targeted therapy. This type of therapy is still evolving at a fast pace and hopefully at least some types of lung cancers will show good response. Currently the prognosis for most lung cancers remains bleak. Increasing awareness of the harmful effects of smoking in all forms and of the need for early diagnosis and early treatment thus becomes all the more important to improve the outcome.
The single most important cause of lung cancer is smoking. About 90% of lung cancers are attributed to smoking, whether active or passive