What Is Lung Cancer? Its Causes, Stages And Prevention

Lung cancer is the leading cause of cancer related deaths in men and the second common in women after breast cancer. Lung cancer kills nearly 158,000 more American people every year than breast, colon and prostate cancers combined.

Nearly 2 million people are diagnosed with lung cancer each year and according to recent numbers the cancer specific 5 year survival rate has been only at 18 percent in 2015. This means only 18 percent people survive for a period of five years after being diagnosed with lung cancer.  More than half of the people with lung cancer die within 1 year after diagnosis.

What Is Lung Cancer 

Lung Cancer is the formation of malignant tumor through carcinogenesis, in the lungs which can than metastasize into other regions of the body.

The two main types of lung cancers are

  • Small Cell Lung Cancer (SCLC)
  • Non-Small Cell Lung Cancer (NSCLC)

Small Cell Lung Cancer SCLC accounts for only 15 percent of lung cases in America and tend to be more responsive to chemotherapy than non-small cell lung cancer. They also advance to the nest stage relatively faster than a NSCLC.

Non-Small Cell Lung Cancer NSCLC accounts for the majority of lung cancers at 85 percent. It can be in the form of an adeno-carcinoma (the most common in US in both sexes), squamous cell carcinoma (accounts for 25 percent of the cases), and large cell carcinoma (accounts for 10 percent of the NSCLC tumors).

At stage 1 it is confined to the lungs, at stage 2 it is near the lymph nodes, at stage 3 the tumor is present in the lymph nodes along with the lungs. Stage 3 can be in the form of 3A (cancer has remained on one side of the chest), or 3B (cancer has spread to the lymph nodes on the opposite side of the chest). At stage 4 the cancer has spread to the other organs in the body.

Lung cancer is rarely detected at stage 1 or 2 due to the non specific symptoms like fatigue and coughing, which the patient often attributes to other causes.

One of the first lung cancer reports was by Adler in 1912, who found 374 cases of primary lung cancer from United States and Western Europe. It was only representative 0.5 percent of all cancer cases. He concluded that it was ‘among rarest forms of disease’.

It was Hruby and Sweany who collected 185,434 autopsy reports from 1897- 1930, which lead them to a conclusion that during these years lung cancer increased disproportionately as compared to the incidence of cancer in general.

Smoking Tobacco And Lung Cancer 

The long effort of proving tobacco usage as a risk factor for lung cancer began with Pear (1938) who showed that cigarette smoking was associated with premature death. Other findings included that tar applied to animal skin produced lung carcinomas.

This led to multiple uncontrolled patient series to highlight the role of smoking with the increase in the incidence of lung cancer. Ochsner and DeBakey in 1941 pronounced with ‘conviction’, that increase in the incidence of lung cancer was due to increase in tobacco smoking.

Doll and Hill, and Wynder and Graham (1950) in separate epidemiological studies established smoking as a causal factor for bronchogenic carcinoma. Wynder and Graham also concluded that there could be a lag of 10 years or more between cessation of smoking and the onset of carcinoma.

The milestone effort to highlight the effects of smoking tobacco was when in 1964, the United States public health service published a report which concluded that cigarette smoking increases the age specific death rates of men by 70 percent but showed a comparatively lesser effect on women.

It also claimed that there is a causal relationship between smoking tobacco and lung cancer. How much a person smokes and how many cigarettes smokes directly increases the person’s risk to develop lung cancer.

 The report observed that a heavy smoker has 20-fold risk for cancer whereas an average smoker has only 10-fold chance of developing lung cancer. Cigarette smoking was also at that time more important than occupational exposure for developing cancer.

Generally smoking was the major cause of chronic bronchitis in the US and male smokers had higher death rate due to coronary heart disease than non smokers.

The publication of that report did decline the per year consumption of cigarettes in US but not by a great degree. Over the years the smoking rates rose from 27.5 percent to 36.4 percent, from 1991 to 1997. The smoking declined to 21.9 percent in 2003 and then again declined to 19.5 percent in 2009.

Cigarette Smoking And Lung Cancer

Tobacco smoking was rare before the 1800s, and was predominantly in the form of pipe smoking and chewing. Cigarette wrapping machinery in mid-1800s changed this by making cigarette rolled tobacco widely available. In 1900 the average number of cigarettes per male adult in a year was only 100.

It rose to 3500 cigarettes per person only in 50 years, and by 1960s it became 4400 cigarettes per person.

Cigarette smoke is made up of aerosol containing gaseous (400-500) and particulate compounds (3500). Mainstream smoke is what the smoker inhales and the side stream smoke components (produced by smoldering of cigarette between puffs) is the source for environmental tobacco smoke (ETS).

Primary smoke is heavily concentrated with tar and nicotine. It also contains potential carcinogens such as polycyclic aromatic hydrocarbons (PAHs), N-nitrosamines, aromatic amines and other organic and inorganic compounds like chromium, arsenic, and benzene.

The international agency for research on Cancer (IARC) has identified potentially 50 carcinogenic compounds in cigarettes. They can also contain radioactive materials like radon and its decay products (polonium and bismuth).

All of these compounds can alter the DNA and RNA in the cells and can activate cancer causing genes or deactivate the cancer suppressors in the cells.

One in nine smokers sooner or later develops lung cancer.


Other forms of smoking tobacco can also increase the risk of lung cancer. A prospective study found that the rate of developing cancer in cigar smokers was at 5.1 as compared to non cigar smokers.

Smoking drugs like marijuana can increase the risk for lung cancer by 8 percent according to a case control study, after adjusting for cigarette usage.

A clear association between inhalant drug usage and lung cancer has not been established.

What Is Lung Cancer? How Do Never Smokers Get It?

If never smokers, people who have smoked less than 100 cigarettes in their lives, are considered separately they would rank as the seventh most common cause of cancer death worldwide.

 It is a staggering statistic and research has seen that non smoker women are affected more than men and it is prevalent more in certain parts of the worlds, such as Asia.

 Although no associations are 100 percent proven to be a cause for lung cancer in non smokers but theorized causes are second hand smoke, radon exposure, and environmental exposures like asbestos, and arsenic.

Other factors can include genetic factors, occupational hazards and health history.

Second Hand Smoke And Lung Cancer

Environmental tobacco smoke (ETS) or second hand smoke often shows dose-dependent relationship between the degree of exposure and the relative risk. A summary analysis of epidemiological studies showed that there is an excess risk for lung cancer of 24 percent in non smokers who lived with a smoker.

IARC and the US environmental protection agency classify ETS as lung carcinogenic compound I terms of its constituents.  ETS can consist of both mainstream and side stream smoke. Various identified carcinogens in ETS are benzene, benzo pyrene, and NNK.


Another study by the American Cancer Society concluded that the relative risk for lung cancer in non smoker women with a smoker husband is at 1.2% while the relative risk for nonsmoking men with smoking wives is at 1.1%.

In a surprising finding, Prikle and colleagues found that 88 percent of non tobacco users had detectable levels of cotinine in their serum which is a metabolite of nicotine. Thus smoking is a public health issue and efforts to control ETS can lead to decreased incidence of Lung Cancer, in theory.

Whats Causes Lung Cancer And What Are Biological Factors

Several studies have shown potential relationships between incidence of lung cancer and biological factors like genetics, age, gender, obesity, ethnicity and other lung diseases.

Studies on familial aggregation, cancer susceptibility genetic markers, and rare mendelian cancer syndromes have shown association of lung cancer with genetic causes. People with lung cancer susceptibility, if they smoke may be at even a higher risk level, for developing the disease. No subgroups have been currently identified as genetically high risk for specific interventions for smoking prevention, cessation, and screening programs.

While smoking prevalence in women is at 18 percent and higher in men at 23 percent. Since 1950, 600 percent increase in lung cancer mortality rate in women has been seen. The overall incidence for age adjusted lung cancer is higher in men than women but the difference is decreasing due to a decrease in incidence of lung cancer in men.

Over the last 40 years the rate for new lung cases has decreased by 28 percent for men and has increased by 98 percent for women. More men are diagnosed each year but more women actually live with the disease.

The difference based on genetic susceptibility of different genders may be dependent upon metabolic activation of lung carcinogens or differences in hormonal levels and nicotine metabolism.

Also, lung cancer is more common in non smoking women than in men. In a study researcher Zang and Wynder found that the proportion of women was 2 times more than that of non smoker men. The reasons for which, still needs a lot of research.

Smoking prevalence is lowest among people aged 65 and above at 9 percent but more than 65 percent of patients who have been diagnosed of lung cancer are 65 and above. The mean age of diagnosis is 70.

Research into these factors also found that diet is responsible for 30 percent of all cancers. Low serum levels of antioxidants have been associated with the development of lung cancer.

Lung Cancer And Environmental Factors

Several environmental factors are associated with development of lung cancer air pollution is one of the most important determinants for lung cancer.

 A case control study showed that relative risk for lung cancer of people exposed to a fixed amount of nitric oxide (measure of traffic air pollutant) was 1.44. Despite multiple studies it is very difficult to find the carcinogenic effect of each individual constituent of air pollution.

What is Lung Cancer

Common pollutants can be nitric oxide, sulphur oxide, and benzene.

Chemicals like radon, nickel, vinyl chloride, silica, cadmium, choloromethyl, ethers, chromium, arsenic and asbestos have been identified by the IARC as carcinogens. Exposure to these elements especially due to occupational hazards can cause lung cancer.

Nearly 5 percent deaths in females (14,300) and 10 percent deaths in males (88,000) can be attributed to 8 occupational lung carcinogens, in the year 2000.

Preventing Lung Cancer

Transformation of normal cells into malignant tumors (Carcinogenesis) can happen due to changes at a molecular level. Changes such as genetic, epigenetic, and DNA damages can be responsible due to any of the above mentioned factors.

Lung cancer can be prevented through control of environmental tobacco smoke, exposure to toxic and cacogenic compounds, along with early detection, chemoprevention, treatment of disease and smoking avoidance.

The major association of lung cancer is with smoking tobacco with an attributable risk of 85 to 90 percent and a relative risk of 20-25 percent.

Prevention of lung cancer therefore can directly be related to cessation of smoking cigarettes. Even though intensive and widespread antismoking campaigns currently work in United States there is a group of 19.8 percent population of America, who are devoted smokers. In 1990 the cessation of smoking halved the number of anticipated lung cancer cases. For men, who ceased smoking at ages 60,50,40,30 years, the risk of lung cancer at the age of 70 went to 10, 6, 3, and 2 percent.

Smokers who stop for more than 15 years have nearly 90 percent risk reduction for lung cancer compared to people who smoke. People who stop before the middle age avoid nearly 90 percent of the attributable risk for lung cancer.

Chemoprevention (a term invented by Sporn and colleagues) describes a preventive measure to treat a person in the early stages of carcinogenesis. It uses specific, natural or unnatural, dietary or pharmacological agents to interfere with the development of cancer cells by preventing DNA damage that initiates a tumor or by stopping the progression of premalignant cells in the lungs.

This strategy can be used to initiate prevention at primary (in people with high risk factors), secondary (in people with disease precursors), or at a tertiary level (in people who have already been treated with cancer before).

Until chemo preventive measures are shown to be efficacious, tobacco usage cessation and control are the best form of preventive measures.

Lung Cancer Took The Life Many Famous People

Lung cancer has taken the life of many, some were those we loved. The most notorious disease on the planet hasn’t been too kind to the famous people who have influenced the masses. The deaths of these personalities brought tears into the eyes of many and some of them were:

  • Walt Disney: The animation virtuoso, who gave us Disney, was a chain smoker and rarely depended on filters. Soon after he hit the 60s, his health started to deteriorate and right after his birthday, Walt died owing to Lung cancer.
  • Paul Newman: The Verdict famed actor, got his final verdict handed to him through the arms of the deadly lung cancer.
  • George Harrison: The man whose artsy fingers did the holy job of creating the mystic music which not only immortalized The Beatles, but also gave him lung cancer. During his later years he blamed the cigarettes in his fingers for his illness.  He was right because eventually he ided owning to lung cancer.
  • Andy Kaufman: The comedian, who struck fame through his infamous altercation with Jerry Lawler on The Late Night Show with David Letterman, failed to laugh and live through his battle with Lung cancer.
  • Dean Martin: “You’re nobody till somebody loves you”, this song continues to strike a chord with anyone who has the honor to listen it. But sadly, the singer faced the same fate as most of the celebrities of that era did. Due to his chain-smoking he died of lung cancer.

Celebrities Who Defeated Cancer:

There’s a saying that if your will is strong enough then even the strongest tides can’t shatter you. Cancer might be the most potent illness ever know to man, but there are few strong humans who dared to look at this disease straight in the eyes.

  • Peter Jeninngs: The acclaimed journalists and the face of ABC for 20 years, didn’t submit to the disease when he first found out about it instead he smiled during the time of adversity and died as a warrior.
  • Steve McQueen: His name still resonates in the pop-culture and why should it not? The famous actor fought lung cancer for the better time of his life.
  • Dane Reeves: Her husband Christopher Reeves, the famous superman, died of cancer and she suffered from the same disease. She spent a significant part of her life advocating for cancer awareness and died in the spirit of one day eradicating this disease.
  • Tammy Messner: The fighter fought for 11 years with a cancer that initially started from her colon and later metastasized to her lungs. One can only imagine the pain she went through, the iron lady didn’t submitted to her imminent death instead she spoke up for all those who suffered from cancer and were fighting an uphill battle.
  • Lance Armstrong: The infamous cyclist is an inspirational fighter. He successfully defeated lung cancer and didn’t just stop there. His organization is currently helping hundreds of cancer patients worldwide.

Co Author : Fizza Akbar 

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