Lung cancer is a serious disease that begins when cells in the lungs start to grow out of control, forming masses called tumors that eventually interfere with how the lungs work. It’s the third most common cancer in the United States and one of the leading causes of cancer-related deaths worldwide, yet advances in treatments have brought new hope and significantly improved survival rates in recent years.
Understanding Lung Cancer
Lung cancer is a disease caused by uncontrolled cell division in your lungs. Normally, your cells divide and make more copies of themselves as part of their natural function. But sometimes, cells develop changes, called mutations, which are alterations in the genetic material of the cell. These mutations cause cells to keep making more copies of themselves when they shouldn’t. When damaged cells divide without control, they create masses or tumors of tissue that eventually prevent your organs from working as they should.[1]
Lung cancer typically starts in the airways, which are tubes called bronchi or bronchioles that carry air in and out of the lungs, or in the small air sacs called alveoli where oxygen enters the bloodstream. From these starting points, the cancer can spread to other parts of the body. It’s important to understand that cancers starting elsewhere in the body and moving to the lungs are usually named for where they began, not as lung cancer itself.[1]
Epidemiology
Lung cancer represents a major global health challenge. In the United States, it is estimated that there are approximately 225,000 new cases of lung cancer diagnosed every year, with around 160,000 deaths occurring annually due to the disease. This makes lung cancer one of the leading causes of cancer-related deaths in the country.[4]
Interestingly, lung cancer was a relatively rare disease at the beginning of the 20th century. Its dramatic rise in the decades that followed can be largely attributed to the increase in smoking among both men and women. Since 1987, lung cancer has been responsible for more deaths in women than breast cancer, highlighting the severity of the disease across genders.[4]
More than 43,000 people are diagnosed with lung cancer every year in the United Kingdom, showing that this is a global concern affecting populations worldwide. The disease mainly affects older people, and it’s rare in those younger than 40. More than four out of ten people diagnosed with lung cancer in the UK are aged 75 or older.[6]
Types of Lung Cancer
There are two main types of lung cancer: non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). These categories refer to what the cancer cells look like when examined under a microscope. Each type grows and spreads in different ways, and treatment approaches differ between them.[5]
Non-small cell lung cancer is the most common form, accounting for about 80 to 85 out of every 100 cases of lung cancer. Within NSCLC, there are several subtypes. Adenocarcinoma is the most common subtype and starts in lung cells that make mucus. These tumors are often found in the outer edges of the lungs and are more likely to be discovered before they spread to other parts of the body. Squamous cell carcinoma is the second most common type and starts in the flat cells lining the airways of the lung. Large cell carcinoma is a very rare type with cells that look very large and round under a microscope, and it can grow and spread very quickly.[1][3]
Small cell lung cancer is less common, representing about 13 to 15 percent of all lung cancer cases. It’s called “small cell” because the cancer cells appear small when examined under a microscope. This type is usually found in the center of a lung and is the most aggressive form of lung cancer. In many cases, it has already spread to other parts of the body by the time it is diagnosed. It grows more quickly and is harder to treat than non-small cell lung cancer.[1][3]
Causes
Smoking is by far the most common cause of lung cancer. It is estimated that approximately 90 percent of lung cancer cases can be attributed to smoking. The disease accounts for more than 70 out of every 100 cases in people who smoke. Smoking involves regularly inhaling many different toxic substances, which damage the cells lining the lungs and airways over time.[2][4]
The risk of developing lung cancer is highest in people who smoke, particularly men. However, the relationship between lung cancer and smoking is complex, involving not just the act of smoking itself but also interactions with environmental and genetic factors. This means there isn’t a simple correlation between the exact number of cigarettes smoked and cancer risk, as individual susceptibility varies.[4]
Although people who have never smoked can develop lung cancer, the connection to smoking is undeniable. Even exposure to secondhand smoke, which is smoke from other people’s cigarettes, cigars, or pipes, increases the risk of lung cancer by 20 to 30 percent. This highlights that you don’t need to be a smoker yourself to be at risk from tobacco smoke.[4][6]
Other environmental and occupational exposures also play a role in causing lung cancer. Exposure to radon, a naturally occurring radioactive gas, is a significant risk factor. Radon exposure, particularly in uranium miners, has been associated with lung cancer development. Asbestos exposure, especially in occupational settings, increases the risk of lung cancer in a way that depends on the dose and varies according to the type of asbestos fiber involved.[4]
Radiation treatment for other cancers, particularly non-Hodgkin’s lymphoma and breast cancer, can also increase the risk of developing lung cancer later in life. Exposure to certain metals such as chromium, nickel, and arsenic, as well as polycyclic aromatic hydrocarbons, has been linked to lung cancer as well. Additionally, certain lung diseases like idiopathic pulmonary fibrosis increase the risk of lung cancer independent of smoking.[4]
Risk Factors
Several factors increase a person’s likelihood of developing lung cancer beyond the primary cause of smoking. People who smoke have the greatest risk, and this risk increases with both the length of time they’ve smoked and the number of cigarettes consumed. Those who quit smoking, however, see their risk decrease over time, though it remains higher than someone who never smoked.[2]
Age is another significant risk factor. Lung cancer mainly affects older people, with the disease being rare in individuals younger than 40. More than four out of ten people diagnosed with lung cancer are aged 75 and older, making advanced age an important consideration when assessing risk.[6]
The risk is further compounded when smoking is combined with exposure to other harmful substances. For example, people who smoke and are also exposed to asbestos face a much higher risk than those exposed to either factor alone. Similarly, exposure to radon gas in homes, particularly when combined with smoking, substantially increases lung cancer risk.[4]
People who are exposed to secondhand smoke regularly, whether at home or in the workplace, have a 20 to 30 percent increased risk of developing lung cancer compared to those not exposed. This makes creating smoke-free environments an important protective measure for everyone, not just smokers.[4]
Certain occupations carry higher risk due to exposure to cancer-causing substances. Workers in industries involving metals like chromium, nickel, and arsenic, or those exposed to polycyclic aromatic hydrocarbons, face increased risk. People with existing lung diseases, such as idiopathic pulmonary fibrosis, also have a higher chance of developing lung cancer regardless of their smoking history.[4]
Symptoms
Lung cancer typically doesn’t cause noticeable symptoms in its early stages. This is one reason why the disease is often discovered at a more advanced stage, which can affect treatment options and outcomes. When symptoms do appear, they usually indicate that the disease has progressed.[2][6]
The most common symptom of lung cancer is a cough that doesn’t go away. This persistent cough is different from the temporary cough that might accompany a cold or flu. Other respiratory symptoms include coughing up blood, even in small amounts, shortness of breath, wheezing, and chest pain. These symptoms occur because the cancer is affecting how the lungs function or because tumors are pressing on airways or other structures in the chest.[2]
When lung cancer spreads to other parts of the body, different symptoms can appear depending on where the cancer has traveled. If it spreads to the bones, people may experience bone pain. Cancer spreading to the brain can cause headaches. Weight loss without trying and loss of appetite are common systemic symptoms that can occur as the body responds to the cancer. Hoarseness, or changes in the voice, can happen if the cancer affects nerves controlling the voice box. Swelling in the face or neck may occur if tumors block blood vessels or lymph nodes in the chest.[2]
Many people with lung cancer also experience unexplained tiredness and general feelings of being unwell. Because these symptoms can be caused by many other, less serious conditions, it’s important to see a doctor if they persist or worry you, especially if you have risk factors for lung cancer like a history of smoking.[2]
Prevention
The most important step you can take to prevent lung cancer is to not start smoking, or if you do smoke, to quit. Since cigarette smoking causes about 80 to 90 percent of lung cancer deaths in the United States, avoiding tobacco is the single most effective prevention strategy. Stopping smoking at any point in your life brings significant health benefits and substantially reduces your risk of developing lung cancer, even if you’ve smoked for many years.[2][22]
Avoiding secondhand smoke is also crucial for prevention. Making your home and car smoke-free protects you and your family from the harmful effects of tobacco smoke. If you spend time in places where others smoke, try to limit your exposure as much as possible.[22]
Testing your home for radon is an important preventive measure. Radon is a naturally occurring radioactive gas that can accumulate in homes and is a leading cause of lung cancer in people who don’t smoke. You can purchase radon test kits or have your home professionally tested. If radon levels are found to be high, there are steps you can take to reduce them and protect your health.[22]
If you work in an environment where you might be exposed to cancer-causing substances like asbestos, metals, or other harmful chemicals, following health and safety guidelines is essential. Use protective equipment provided by your employer and follow all recommended safety procedures to minimize your exposure to these carcinogens.[22]
For people at high risk of lung cancer, screening may help detect the disease at an early stage when treatment is more likely to be effective. As of 2021, screening recommendations include annual lung cancer screening using low-dose computed tomography (CT) for adults aged 50 to 80 who have a 20 pack-year smoking history and currently smoke or have quit within the past 15 years. A pack-year is calculated by multiplying the number of packs of cigarettes smoked per day by the number of years of smoking.[12]
Pathophysiology
Lung cancer develops through a process where normal cells in the lungs undergo changes that transform them into cancer cells. The lungs are spongy organs in the chest responsible for bringing oxygen into the body and removing carbon dioxide, a waste product. They contain airways called bronchi and bronchioles, which are tubes that carry air in and out, and tiny air sacs called alveoli where gas exchange happens between the air and blood.[1]
Cancer begins when cells in these structures develop mutations in their genetic material. These mutations can be caused by exposure to carcinogens like tobacco smoke, radiation, or other harmful substances, or they can occur spontaneously. The mutations disrupt the normal controls that regulate cell growth and division. Instead of following their usual life cycle of growing, dividing, and dying in an orderly way, the mutated cells begin to divide uncontrollably.[1]
As these abnormal cells accumulate, they form a mass or tumor. In the early stages, the cancer may be confined to the original site, such as the lining of a bronchus or within lung tissue. As the tumor grows, it can invade nearby tissue and destroy normal lung structure. The cancer can grow into the walls of airways, making them narrower and causing symptoms like coughing and shortness of breath. Tumors can also press on blood vessels or nerves in the chest.[1][3]
Cancer cells can break away from the original tumor and travel through the bloodstream or lymphatic system to other parts of the body. This process is called metastasis. The lymphatic system is a network of vessels and nodes that helps fight infection and remove waste from tissues. Lung cancer commonly spreads first to nearby lymph nodes in the chest. From there, or directly through the bloodstream, cancer cells can reach distant organs such as the brain, bones, liver, or the other lung. When cancer spreads, it forms new tumors in these locations, which interfere with the function of those organs.[1]
The type of lung cancer affects how it grows and spreads. Small cell lung cancer tends to grow and spread more quickly than non-small cell lung cancer. By the time small cell lung cancer is diagnosed, it often has already spread beyond the lungs. Non-small cell lung cancer generally grows more slowly, though this can vary depending on the specific subtype and individual characteristics of the tumor.[1][3]
The body’s normal defenses struggle to control cancer cells because these cells have developed ways to evade or suppress immune responses. They can also stimulate the growth of new blood vessels to supply themselves with nutrients and oxygen, a process called angiogenesis. All these changes at the cellular and tissue level explain why lung cancer can be so difficult to treat once it becomes advanced.[1]
