Squamous Cell Carcinoma of Lung

Squamous cell carcinoma of the lung is the second most common type of lung cancer after adenocarcinoma, representing about 25-30% of all lung cancer cases. This type of cancer forms when thin, flat cells lining the airways become damaged and multiply uncontrollably, most often in the central part of the lung.

Table of contents

• What is squamous cell carcinoma of the lung?
• Where the cancer develops
• Causes and risk factors
• Signs and symptoms
• How it is diagnosed
• Stages of the disease
• Treatment approaches
• Outlook and survival

What is squamous cell carcinoma of the lung?

Squamous cell carcinoma of the lung, also called epidermoid carcinoma, is a type of cancer that starts in the squamous cells.^[4] These are thin, flat cells that line the airways of your lungs, much like the lining inside a pipe. They create a protective barrier between the air you breathe and the lung tissue itself.^[4]

This cancer develops when these cells become damaged or abnormal and begin to multiply out of control, eventually forming a tumor.^[4] Over time, the tumor cells can spread to other parts of your body through the constant flow of blood and other fluids through the lungs.^[5]

Squamous cell carcinoma is one type of non-small cell lung cancer (NSCLC), which is the most common category of lung cancer. The other main types of NSCLC are adenocarcinoma and large cell carcinoma.^[7] Among NSCLC cases, adenocarcinoma is the most common, followed by squamous cell carcinoma.^[2]

Where the cancer develops

The majority of squamous cell carcinoma cases start in the center of the lung, near the main airways such as the left or right bronchus (the large breathing tubes that connect your windpipe to your lungs).^[2] This central location is different from some other lung cancers, like adenocarcinoma, which more often develop on the outer edges of the lungs.^[5]

Because squamous cell tumors develop in the central airways, they may cause certain symptoms, such as coughing up blood, at an earlier stage than tumors in other locations.^[5] This central position can sometimes help with earlier detection of the disease.

Causes and risk factors

Smoking cigarettes is by far the leading cause of squamous cell carcinoma of the lung. In fact, squamous cell carcinoma is more strongly linked to smoking than any other type of lung cancer.^[2] About 80% of lung cancer cases in men and 90% in women are associated with smoking.^[2] Squamous cell carcinomas make up 25-30% of all lung cancers and are the most common lung cancers found in smokers.^[4]

It is very rare for people who have never smoked to develop squamous cell carcinoma of the lung.^[4] However, the risk of developing this cancer decreases the longer a person has been smoke-free.^[4] Cigar and pipe smoking carry nearly the same risk as cigarette smoking.^[5]

Other important risk factors include:

• Secondhand smoke: People who breathe in tobacco smoke from others have an increased risk of lung cancer, even if they don’t smoke themselves.^[2]
• Radon exposure: Radon is a colorless, odorless radioactive gas that forms in the ground and can seep into buildings. It is the second leading cause of lung cancer.^[5]
• Asbestos exposure: People exposed to asbestos on the job (such as miners, construction workers, or shipyard workers) have a higher risk of lung cancer. The risk is even greater for people who also smoke.^[5]
• Other workplace exposures: Occupational exposure to uranium, arsenic, vinyl chloride, nickel chromates, coal products, mustard gas, gasoline, diesel exhaust, and certain metal particles can increase risk.^[2]
• Age and family history: Older age and having family members with lung cancer can also affect your risk.^[2]

Signs and symptoms

Like other types of lung cancer, many people with squamous cell carcinoma do not experience symptoms in the early stages.^[4] However, as the disease progresses, symptoms may appear, sometimes earlier than with other lung cancer types because of the tumor’s central location.

Common symptoms include:

• A persistent cough that doesn’t go away^[2]
• Coughing up blood^[4]
• Shortness of breath^[2]
• Chest pain^[2]
• Wheezing^[2]
• Hoarseness^[2]
• Recurring chest infections, such as bronchitis or pneumonia^[2]
• Unexplained weight loss^[2]
• Loss of appetite^[2]
• Fatigue^[2]
• Bone pain (if the cancer has spread)^[4]

If you experience any of these symptoms, especially if you have a history of smoking or other risk factors, it’s important to see your doctor for evaluation.

How it is diagnosed

When squamous cell carcinoma of the lung is suspected, doctors use several tests to confirm the diagnosis and determine how far the cancer has spread.

The diagnostic process typically includes:

• Medical history and physical examination: Your doctor will ask about your symptoms, smoking history, and other risk factors, and perform a physical exam.^[2]
• Imaging tests: A computed tomography (CT) scan is frequently used first to look at the lungs and detect tumors large enough to be seen.^[2] Other imaging tests may include chest X-rays, MRI scans, PET scans, or bone scans.^[6]
• Biopsy: To confirm the diagnosis, doctors need to examine a sample of tissue from the tumor under a microscope. This is called a biopsy.^[7] The sample can be obtained through procedures like bronchoscopy (using a thin tube inserted through the nose or mouth into the airways), needle biopsy, or other methods.^[2]
• Laboratory tests: Blood tests and examination of cells from sputum (mucus coughed up from the lungs) may also be performed.^[2]
• Molecular testing: Additional tests may be done on the tumor tissue to look for specific genetic changes that could affect treatment options.^[6]

These tests help doctors determine the exact type of lung cancer, its stage, and the best treatment approach for each individual patient.

Stages of the disease

Cancer staging helps doctors understand how far the cancer has spread and plan the best treatment. Squamous cell carcinoma of the lung is staged from 0 to IV, based on the size of the tumor, whether it has spread to lymph nodes, and whether it has spread to other parts of the body.^[6]

Stage 0: The cancer is found only in the top lining of the lung and has not spread outside the lung.^[4]

Stage I: The cancer has not spread to the lymph nodes or other parts of the body. The stage is further divided into IA and IB based on the size of the tumor and whether it has grown into the lung lining.^[4]

Stage II: The cancer is larger than Stage I and has begun to spread to nearby lymph nodes or tissues, but not to distant organs. The stage is divided into IIA and IIB based on tumor size, location, and lymph node involvement.^[4]

Stage III: The cancer may be difficult to remove with surgery. It is divided into IIIA, IIIB, and IIIC based on tumor size, location, and how much it has spread to nearby structures and lymph nodes.^[4]

Stage IV: The cancer has spread (metastasized) to other areas of the body outside the lungs, such as the liver, bones, brain, or the other lung.^[4] This is the most advanced stage.

Unless squamous cell carcinoma is diagnosed and treated early, it often spreads throughout the body because cancer cells can travel through the blood and lymph fluid that constantly flow through the lungs.^[5]

Treatment approaches

Treatment for squamous cell carcinoma of the lung depends on the stage of the cancer and the patient’s overall health. Treatment usually involves a combination of different approaches.^[2]

Main treatment options include:

• Surgery: Surgery is the treatment of choice for patients with early-stage disease (stages I through IIIA) when the tumor can be removed.^[15] The surgeon removes the tumor along with some surrounding healthy tissue and nearby lymph nodes.
• Chemotherapy: Chemotherapy uses drugs to kill cancer cells throughout the body. It may be given before surgery to shrink tumors, after surgery to kill any remaining cancer cells, or as the main treatment for advanced cancer.^[2] Since the early 2000s, platinum-based chemotherapy has been the standard first-line treatment for advanced squamous cell carcinoma.^[14]
• Radiation therapy: Radiation uses high-energy beams to kill cancer cells. It is a reasonable option for patients who cannot have surgery and may be combined with chemotherapy.^[15]
• Targeted therapy: These are drugs that target specific genetic changes in cancer cells. Targeted therapy plays an increasingly important role in treating advanced lung cancer.^[15]
• Immunotherapy: This treatment helps your own immune system fight cancer. In 2022, the drug nivolumab was approved for use before surgery in combination with chemotherapy for certain patients with resectable (removable) squamous cell carcinoma.^[15]

Patients with advanced cancer may also receive palliative care alongside their cancer treatment. Palliative care focuses on relieving symptoms, improving quality of life, and providing emotional support. Research shows that patients with advanced lung cancer who receive early palliative care alongside standard treatment have better quality of life and may even live longer.^[15]

Patients who have had surgery for lung cancer often receive additional chemotherapy afterward to reduce the risk of the cancer coming back.^[15]

Outlook and survival

The outlook for squamous cell carcinoma of the lung depends on several factors, including the stage at diagnosis, the patient’s overall health, and how well the cancer responds to treatment.

In general, non-small cell lung cancers like squamous cell carcinoma tend to have a better prognosis than small cell lung cancer because they are more likely to be contained in one area, making successful treatment more possible.^[5]

However, lung cancer remains serious. Many cases are not diagnosed until they have already spread, which makes treatment more challenging. Early detection through screening programs for people at high risk (such as current or former smokers) can improve outcomes by finding cancer at more treatable stages.^[6]

Advances in treatment have led to significant improvements in recent years. New therapies, including targeted drugs and immunotherapy, have caused a notable decline in lung cancer deaths.^[6] Ongoing research continues to develop better treatment strategies for advanced squamous cell carcinoma of the lung.^[14]

Each person’s situation is unique, and survival depends on many individual factors. Your healthcare team can provide the most accurate information about your specific outlook and help you understand your treatment options.