Squamous cell carcinoma of the lung is one of the most common types of lung cancer, developing in the thin, flat cells that line the airways deep inside the lungs. Strongly linked to smoking, this cancer typically starts in the central part of the lung and can cause serious health challenges if not detected and treated early.

Understanding Squamous Cell Carcinoma of the Lung

Squamous cell carcinoma of the lung, also known as epidermoid carcinoma, is a type of non-small cell lung cancer, which refers to a group of lung cancers that behave differently from small cell lung cancer. Within the non-small cell category, squamous cell carcinoma is the second most common form, accounting for approximately 25 to 30 percent of all non-small cell lung cancer cases.^[2][4] The name comes from the type of cells where the cancer begins—squamous cells, which are thin and flat, lining the airways like the interior coating of a pipe. These cells act as a protective barrier between the air flowing through the lungs and the lung tissue itself.^[4]

The disease develops when these squamous cells become damaged or abnormal and begin to multiply uncontrollably, forming a tumor. The majority of squamous cell carcinoma cases start in the central portion of the lung, near the main airways such as the left or right bronchus (the large air passages leading from the windpipe into the lungs).^[2][4] This central location distinguishes squamous cell carcinoma from other lung cancer types, like adenocarcinoma, which more commonly develops on the outer edges of the lungs. Because of its location near major airways, squamous cell carcinoma may produce noticeable symptoms at an earlier stage compared to cancers developing in the lung’s periphery.^[5][4]

How Common Is Squamous Cell Carcinoma of the Lung?

Lung cancer is one of the most common cancers worldwide and remains the leading cause of cancer deaths globally.^[6] Among all lung cancers, approximately 85 to 90 percent are classified as non-small cell lung cancer.^[2] Of these non-small cell cases, squamous cell carcinoma represents about 30 percent, making it a significant health concern affecting thousands of people each year.^[2][5]

Interestingly, patterns in lung cancer types have shifted over the decades. While adenocarcinoma has become the most common type of non-small cell lung cancer overall, particularly in women, squamous cell carcinoma remains the second most common.^[2] This change is thought to be related to evolving patterns of cigarette smoking, though researchers note there is no definitive proof of this connection. What is clear is that squamous cell carcinoma is much more strongly associated with smoking than any other type of non-small cell lung cancer, and it is very uncommon to find squamous cell carcinoma in people who have never smoked.^[2][4]

What Causes Squamous Cell Carcinoma of the Lung?

The principal cause of squamous cell carcinoma of the lung is tobacco smoking. Cigarette smoking is by far the leading risk factor for this disease, with approximately 80 percent of lung cancer cases in men and 90 percent in women being associated with smoking.^[2] In fact, cigarette smokers are 13 times more likely to develop lung cancer compared to people who have never smoked.^[5] Cigar and pipe smoking carry nearly the same risk as cigarette smoking when it comes to causing lung cancer.^[5]

Squamous cell carcinoma is more closely linked to smoking than any other type of non-small cell lung cancer, making it extremely rare in nonsmokers.^[2][4] The harmful chemicals in tobacco smoke damage the cells lining the airways. Over time, repeated exposure causes these cells to undergo abnormal changes, eventually leading to cancer. The transformation from normal cells to cancerous ones is a gradual process driven by the toxic substances found in tobacco.

Risk Factors for Developing This Cancer

While smoking is the dominant risk factor, several other exposures and circumstances can increase a person’s likelihood of developing squamous cell carcinoma of the lung. Understanding these risk factors can help individuals recognize their vulnerability and take preventive action where possible.

Exposure to secondhand smoke significantly raises lung cancer risk in nonsmokers. People who inhale fumes from cigarettes, cigars, and pipes smoked by others face an elevated risk of developing lung cancer, including squamous cell carcinoma.^[5] This is particularly concerning for family members or coworkers of smokers who spend considerable time in smoke-filled environments.

Radon gas exposure is the second leading cause of lung cancer after smoking. Radon is a colorless, odorless radioactive gas that forms naturally in the ground and can seep into the lower floors of homes and buildings, as well as contaminate drinking water.^[5] While it is unclear whether elevated radon levels contribute to lung cancer in nonsmokers, radon exposure definitely contributes to lung cancer risk in smokers and in people who regularly breathe high concentrations of the gas at work, such as miners. Testing home radon levels with a simple kit can help identify and address this hidden hazard.^[5]

Occupational exposures to various cancer-causing substances also increase risk. Asbestos, a mineral historically used in insulation, fireproofing materials, floor and ceiling tiles, and automobile brake linings, poses a significant danger. Workers exposed to asbestos on the job—including miners, construction workers, shipyard workers, and some auto mechanics—have higher-than-normal lung cancer rates.^[5] Additionally, people who live or work in buildings containing deteriorating asbestos materials face increased risk. The combination of asbestos exposure and smoking is particularly dangerous, multiplying cancer risk far beyond what either factor would cause alone.^[5]

Other workplace carcinogens that raise lung cancer risk include uranium, arsenic, vinyl chloride, nickel chromates, coal products, mustard gas, chloromethyl ethers, gasoline, and diesel exhaust.^[5] Workers in industries handling these substances should follow all safety protocols and use protective equipment.

Beyond environmental exposures, certain personal factors also play a role. Age is one consideration, as lung cancer risk increases with advancing years. Family history matters too—having relatives with lung cancer may slightly increase one’s own risk.^[2] Importantly, for people who have smoked, the risk of developing squamous cell carcinoma decreases the longer a person has been smoke-free, offering hope and motivation for quitting at any age.^[4]

Signs and Symptoms to Watch For

Like other types of lung cancer, squamous cell carcinoma often does not cause noticeable symptoms in its earliest stages. Many people have no symptoms when the disease first develops, which is why screening is so important for high-risk individuals. However, as the cancer progresses, symptoms tend to appear, and because of its central location in the airways, squamous cell carcinoma may cause symptoms at an earlier stage than cancers located on the lung’s outer edges.^[4][5]

Common symptoms of squamous cell carcinoma and other non-small cell lung cancers include a persistent cough that does not go away. This cough may worsen over time and can be different from a typical cough caused by a cold or respiratory infection.^[2] Chest pain is another frequent complaint, ranging from mild discomfort to sharp pain that may worsen with breathing or coughing.

Shortness of breath, or feeling like you cannot catch your breath during normal activities, is a significant warning sign.^[2] Coughing up blood, even in small amounts, is a particularly concerning symptom that should prompt immediate medical attention.^[2][4] This symptom can appear earlier in squamous cell carcinoma compared to some other lung cancer types.

Other respiratory symptoms include wheezing (a whistling sound when breathing) and hoarseness or changes in the voice.^[2] Recurring chest infections such as bronchitis or pneumonia that keep coming back despite treatment can also signal an underlying problem.^[2][4]

Beyond respiratory complaints, squamous cell carcinoma can cause more general symptoms that affect overall health. Unexplained weight loss—losing weight without trying—is common in many cancers, including lung cancer.^[2][4] Loss of appetite often accompanies this weight loss. Fatigue, or feeling extremely tired and lacking energy even with adequate rest, is another frequent symptom.^[2] If the cancer has spread to the bones, bone pain may develop.^[4]

Prevention Strategies

Preventing squamous cell carcinoma of the lung centers primarily on avoiding tobacco exposure. Because smoking is responsible for the vast majority of cases, never starting to smoke is the single most important preventive measure. For people who currently smoke, quitting is the most powerful action they can take to reduce their risk. Even for long-term smokers, quitting significantly lowers the chance of developing lung cancer, and the risk continues to decrease the longer a person remains smoke-free.^[4]

Healthcare providers can recommend various strategies for quitting smoking, including counseling, medications, and nicotine replacement products such as patches or gum.^[8] Many people find that combining different approaches works best, and seeking support increases the chances of successfully quitting. While quitting can be challenging, the health benefits begin almost immediately and grow over time.

Avoiding secondhand smoke is also crucial. If you live or work with smokers, encouraging smoke-free environments protects everyone’s health. In homes, establishing no-smoking policies and ensuring smokers take their habit outdoors reduces exposure for all household members.

Testing for and mitigating radon exposure in the home is another important preventive step. Inexpensive radon testing kits are available at hardware stores and online. If testing reveals elevated radon levels, professional radon mitigation systems can be installed to reduce concentrations to safe levels.^[5]

For people working in industries with exposure to known carcinogens like asbestos, uranium, arsenic, or other harmful substances, following all workplace safety guidelines is essential. This includes using proper protective equipment such as respirators or masks, working in well-ventilated areas, and following decontamination procedures to avoid bringing hazardous materials home on clothing or skin.^[5]

Lung cancer screening is recommended for people at high risk. While screening does not prevent cancer, it can detect the disease at earlier, more treatable stages, significantly improving survival chances.^[6] Screening typically involves low-dose computed tomography (CT) scans. Healthcare providers can help determine whether screening is appropriate based on individual risk factors such as age, smoking history, and exposure history.

How the Disease Develops in the Body

Understanding the biological changes that occur when squamous cell carcinoma develops helps clarify why the disease behaves as it does. The lungs are a pair of cone-shaped organs in the chest responsible for bringing oxygen into the body and removing carbon dioxide. Each lung consists of sections called lobes—the left lung has two lobes, while the right lung has three.^[7]

Air enters through the windpipe, or trachea, which divides into two large tubes called bronchi—one leading to each lung. The bronchi branch into progressively smaller tubes called bronchioles, which eventually end in tiny air sacs called alveoli where oxygen and carbon dioxide are exchanged with the bloodstream.^[7] The entire system is lined with specialized cells, including the flat squamous cells where this type of cancer originates.

When harmful substances like tobacco smoke repeatedly damage these squamous cells, the cells undergo changes at the genetic level. Normally, cells divide and reproduce in an orderly, controlled fashion to maintain healthy tissues. However, when cells acquire certain mutations—changes in their genetic material—they may begin dividing uncontrollably. Instead of dying when they should, these abnormal cells keep multiplying, eventually forming a mass of tissue called a tumor.^[6]

In squamous cell carcinoma, this process typically begins in the central airways near the bronchi. As the tumor grows, it can partially or completely block the airway, explaining symptoms like persistent cough, shortness of breath, and recurring infections. The tumor may also invade surrounding lung tissue and structures, causing chest pain.

The lungs’ rich blood and lymphatic supply, while essential for normal function, also creates pathways for cancer cells to spread. Cancer cells can break away from the original tumor and travel through these fluid channels to other parts of the body—a process called metastasis.^[5] Squamous cell carcinoma commonly spreads to nearby areas first, such as the lymph nodes around and between the lungs, the chest wall, neck, esophagus, and the protective sac around the heart. If not treated, it can eventually spread to distant organs including the liver, bones, adrenal glands, and brain.^[5]

The stage at which cancer is diagnosed—meaning how large the tumor is and how far it has spread—significantly affects treatment options and prognosis. Cancers caught when still localized to the lung are generally more treatable than those that have spread widely throughout the body.