Adenosquamous Cell Lung Cancer

Adenosquamous cell lung cancer is a rare and aggressive type of lung cancer that contains characteristics of both lung adenocarcinoma and squamous cell carcinoma. This uncommon cancer accounts for only a small percentage of all lung cancer cases but requires specialized attention due to its unique features and treatment challenges.

Table of contents

• What Is Adenosquamous Cell Lung Cancer
• Classification and Medical Codes
• Affected Anatomy
• Causes and Risk Factors
• Symptoms
• Diagnosis
• Prognosis and Survival
• Treatment Options

What Is Adenosquamous Cell Lung Cancer

Adenosquamous cell lung cancer (ASC) is a relatively rare subtype of non-small cell lung cancer (NSCLC), which is the broader category that includes most lung cancers other than small cell types. ASC is defined as a cancer that contains components of both lung adenocarcinoma (cancer arising from cells that produce mucus) and lung squamous cell carcinoma (cancer arising from flat cells lining the airways).^[1]

According to current medical classification standards, a lung tumor must contain at least 10% by volume of each component—both squamous cell carcinoma and adenocarcinoma cells—to be classified as adenosquamous carcinoma.^[2] Although ASC has biological characteristics of both adenocarcinoma and squamous cell carcinoma, it is not simply a combination of these two components. Instead, it represents a distinct disease entity with its own behavior and treatment considerations.^[1]

ASC accounts for approximately 1.6% of all NSCLC cases, making it quite uncommon.^[3] This rarity means that many patients and even some healthcare providers may have limited experience with this specific cancer type. The cancer is known for being more aggressive than pure adenocarcinomas or squamous cell carcinomas of the lung.^[4]

Classification and Medical Codes

Adenosquamous cell lung cancer belongs to a family of lung cancers that have been classified in increasingly detailed ways over recent decades. Before the mid-1900s, all lung cancers were treated as a single disease. Today, medical science recognizes that lung cancers are an extremely diverse family of diseases with widely varying characteristics, particularly in how they respond to different treatments.^[2]

Under the World Health Organization classification system, adenosquamous carcinoma is recognized as one of eight major groups of lung carcinomas. The other major groups include squamous cell carcinoma, small cell carcinoma, adenocarcinoma, large cell carcinoma, sarcomatoid carcinoma, carcinoid tumor, and salivary gland-like carcinoma.^[2]

lung adenosquamous carcinoma, ASC, adenosquamous lung carcinoma, AdSqLC

Affected Anatomy

Adenosquamous cell lung cancer arises from the tissue of the lungs, specifically from the epithelial cells—the cells that line the surfaces of the respiratory system from the central bronchi (the main airways) to the terminal alveoli (tiny air sacs where oxygen exchange occurs).^[1]

• Lungs
• Bronchi (airways)
• Bronchioles (smaller airways)
• Alveoli (air sacs)

The specific location where the cancer develops can vary. The squamous cell component typically originates near the central bronchi, while the adenocarcinoma component usually develops in peripheral lung tissue.^[1] Because ASC contains both components, the tumor can display characteristics related to both central and peripheral lung locations.

Causes and Risk Factors

While the exact cause of adenosquamous cell lung cancer remains uncertain, several risk factors have been identified that increase the likelihood of developing this disease.^[4]

Smoking is the primary risk factor for most lung cancers, including ASC. Research shows that around 80% of squamous cell lung carcinoma cases in men and 90% of cases in women are linked to tobacco smoke. In fact, squamous cell carcinoma lung cancer is more closely linked to smoking than any other type of lung cancer, and since ASC contains this squamous component, smoking plays a significant role in its development.^[4]

Other important risk factors include:^[4]

• Exposure to secondhand smoke from cigarettes, pipes, or cigars
• Exposure to asbestos, a mineral fiber once commonly used in construction and manufacturing
• Exposure to radon, a naturally occurring radioactive gas
• Exposure to other industrial substances such as arsenic, chromium, beryllium, and nickel
• Previous radiation therapy to the chest area
• Family history of lung cancer

It’s important to note that these toxic substances are all considered carcinogens—cancer-causing agents. For example, asbestos fibers can damage lung tissues and may trigger cancer development 10 to 50 years after the initial exposure.^[4]

Symptoms

The symptoms of adenosquamous carcinoma of the lung are similar to those seen with other forms of lung cancer. Many patients may not experience noticeable symptoms in the early stages of the disease.^[4]

Common symptoms include:

• Persistent cough that doesn’t go away
• Shortness of breath or difficulty breathing
• Chest pain
• Hemoptysis—coughing up blood
• Fatigue or weakness
• Unexplained weight loss
• Frequent infections such as bronchitis or pneumonia

Because these symptoms can also occur with many other respiratory conditions, it’s essential to seek medical evaluation if they persist or worsen over time.

Diagnosis

Diagnosing adenosquamous cell lung cancer is extremely difficult before surgery. The most effective means for adequate diagnosis of ASC is examination of surgically removed tissue by a pathologist—a doctor who specializes in studying diseased tissues under a microscope.^[1]

The diagnostic process typically involves multiple steps and different types of tests:^[4]

Imaging studies are usually the first step. These may include chest X-rays or CT scans (computed tomography scans) that use X-rays and computer processing to create detailed images of the lungs. These tests help identify abnormal masses or nodules that might indicate cancer.

Bronchoscopy is a procedure in which a thin, flexible tube with a camera is inserted through the nose or mouth and down into the airways. This allows doctors to view the inside of the lungs and collect tissue samples for testing.

Biopsy is the definitive diagnostic step. This involves removing a sample of tissue from the suspicious area for examination under a microscope. The biopsy can be obtained through needle aspiration (using a needle to withdraw tissue) or through surgical methods. For ASC specifically, the pathologist must identify both adenocarcinoma and squamous cell carcinoma components, with each making up at least 10% of the tumor.^[2]

One unique challenge with ASC is that an interesting pattern has been observed: PD-L1 expression (a protein that affects immune response) was significantly higher in the squamous component versus the glandular component when these were analyzed separately in ASC tumors.^[5] This biological difference between the two components within the same tumor highlights the complexity of this disease.

Prognosis and Survival

Adenosquamous cell lung cancer is associated with a poorer prognosis than pure adenocarcinomas or squamous cell carcinomas of the lung due to its aggressive nature.^[4] However, survival depends heavily on the stage at which the cancer is diagnosed and treated.

For patients who undergo surgical removal of the tumor, studies have shown varied survival rates. One study found that the cumulative postoperative 3-year survival rate was 56% and the 5-year survival rate was 48%.^[3] However, overall survival was significantly lower in ASC patients compared to patients with pure adenocarcinoma who were operated on during the same period.^[3]

Research has identified several factors that influence prognosis:^[3]

The predominant histological subtype—whether the tumor contains more adenocarcinoma or squamous cell features—appears to matter. Patients with ASC containing acinar predominant adenocarcinoma had better survival than those with non-acinar predominant ASC.

Gender, the specific pathological subtype, and TNM staging (a system that describes the size and spread of the tumor) have been identified as independent prognostic factors through statistical analysis.^[3]

For early stage disease (stage I), studies from large databases have provided additional insight. The mean tumor size for stage I ASC was approximately 26.2 mm, and patients included both stage IA and stage IB cases.^[6]

Treatment Options

Treatment for adenosquamous cell lung cancer depends on multiple factors including the stage of disease, the patient’s overall health, and specific characteristics of the tumor. Because ASC is a rare variant of NSCLC with poorer prognosis and fewer established treatment options than more common variants, ongoing research continues to identify the most effective approaches.^[5]

Surgery

For patients with early stage disease, surgical removal of the tumor is a primary treatment option. Various surgical procedures may be used, including lobectomy (removal of a lobe of the lung), segmentectomy (removal of a segment of the lung), or pneumonectomy (removal of an entire lung).^[4] Research indicates that patients who received surgery combined with adjuvant therapy generally had better outcomes compared to those who received only chemotherapy.^[6]

Chemotherapy

Platinum-based chemotherapy is a mainstay treatment for ASC. For stage III patients with ASC, platinum-based postoperative adjuvant chemotherapy for at least four cycles can significantly improve survival.^[1] Chemotherapy uses drugs to kill cancer cells and may be given before surgery to shrink the tumor or after surgery to eliminate any remaining cancer cells.^[4]

Targeted Therapy

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) such as erlotinib and gefitinib can be effective therapeutic strategies for advanced ASC in patients whose tumors have EGFR mutations—specific genetic changes that make the cancer cells vulnerable to these drugs.^[1] These targeted therapies work by blocking specific molecules that cancer cells need to grow and spread.^[4]

However, research on other targeted therapies remains limited. Studies of crizotinib (a drug targeting ALK mutations) in the treatment of patients with ASC are very limited.^[1] Additionally, research has shown that PD-L1 expression did not correlate with EGFR, KRAS, or ALK mutations in lung ASCs.^[5]

Immunotherapy

Immune checkpoint blockade therapy may be a potential treatment choice for ASC patients.^[1] Immunotherapy works by helping the body’s own immune system fight the cancer.^[4]

Research has shown promising results with immune checkpoint inhibitors for advanced lung ASC. In one study of 38 patients with previously treated lung ASC, treatment with immune checkpoint inhibitors produced an objective response rate of 23.7% and a disease control rate of 86.8%. The median progression-free survival was 5.47 months and median overall survival was 24.10 months.^[9]

Interestingly, among patients successfully evaluated for PD-L1 expression status, those with PD-L1-positive tumors showed better response rates compared to PD-L1-negative patients. The objective response rate for PD-L1-positive patients was 36.4% with a 100% disease control rate, while PD-L1-negative patients showed a 0% objective response rate and 50% disease control rate.^[9]

Research suggests that anti-PD-L1 therapy is a promising treatment option in lung ASC cases where PD-L1 is upregulated and EGFR mutations are present.^[5]

Radiation Therapy

Radiation therapy uses high-energy rays to target and kill cancer cells. It can be used alone or in combination with other treatments.^[4]

Additional Supportive Measures

Patients with advanced disease may benefit from various supportive measures to improve quality of life and manage symptoms. These are sometimes referred to as palliative care approaches and focus on comfort rather than cure.^[4]