Types of Lung Cancer: NSCLC and SCLC

Lung cancer is classified by where it begins and the features of the cancer cells. The two main types of lung cancer are non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). Knowing the types of lung cancer helps explain how these cancers may behave.

Non-small cell lung cancer includes several subtypes, such as adenocarcinoma, squamous cell carcinoma and large cell carcinoma. Small cell lung cancer is a different type that generally grows and spreads more quickly. NSCLC is the most common type of lung cancer, while SCLC is less common.

The cancer type does not describe how far the disease has spread. That information is called the lung cancer stage. Both type and stage help the healthcare team make treatment decisions and develop an appropriate treatment plan.

What Are the Main Types of Lung Cancer?

The two main types of lung cancer differ in their appearance, behaviour and classification.

These are broad patterns. The behaviour of an individual cancer can vary according to its subtype, stage and molecular features.

Population registries may report lung and bronchus cancer together, so proportions vary by population and classification. Adenocarcinoma is the most common type of NSCLC. Small cell carcinoma is the most common type of SCLC.

Non-Small Cell Lung Cancer

Non-small cell lung cancer (NSCLC) is an umbrella term for several cancers that share certain cellular features. It accounts for about 80% to 85% of primary lung cancers and is the most common type of primary lung cancer.

NSCLC may begin in different cells within the airways or the air sacs of the lungs. Its three principal subtypes are adenocarcinoma, squamous cell carcinoma and large cell carcinoma. These types of lung cancer are named for the cell types and features seen under a microscope.
 

Adenocarcinoma

Lung adenocarcinoma begins in gland-forming cells that may produce mucus. These cells are often found near the alveoli, which are the small air sacs where oxygen enters the bloodstream.

Adenocarcinoma is the most common form of NSCLC. It often develops in the outer parts of the lung and can occur in people who smoke, previously smoked or have never smoked.

Smoking remains an important lung cancer risk factor, but a person’s smoking history cannot determine the cancer type. Read more about lung cancer in non-smokers.
 

Squamous Cell Carcinoma

Squamous cell lung carcinoma begins in flat cells lining the airways. It often develops in or near the bronchi, which are the larger tubes that carry air into the lungs. These flat cells may become abnormal and form a squamous cell tumour. Squamous cell carcinoma accounts for about one quarter of lung cancers worldwide, although the proportion varies by population and sex.

This subtype has a strong association with tobacco exposure. However, a biopsy is still needed to distinguish squamous cell carcinoma from other lung cancers.
 

Large Cell Carcinoma

Large cell lung carcinoma is an uncommon form of NSCLC. The cancer cells appear large and lack the features needed to classify them as adenocarcinoma, squamous cell carcinoma or neuroendocrine carcinoma.

Large cell carcinoma is a diagnosis of exclusion. This means the pathologist makes the diagnosis after ruling out more specific subtypes. Current pathology guidance restricts this diagnosis to thoroughly sampled resection specimens (tissue removed during surgery), because a small biopsy cannot reliably exclude a more specific cancer type.

Large cell carcinoma is different from large cell neuroendocrine carcinoma, despite the similar names.
 

Less Common NSCLC Subtypes

Less common forms of NSCLC include:

• Adenosquamous carcinoma, a less common type containing both glandular and squamous cancer cells
• Sarcomatoid carcinoma, a group of uncommon tumours with epithelial and spindle-shaped or giant cells
• Salivary gland-type carcinomas, which are rare types of lung cancer that may begin in glands within the airways
• Unclassified carcinoma, when the available sample does not show enough features for a more specific diagnosis

Detailed classification depends on the lung tissue available and the results of laboratory testing. Lung cancer research continues to refine classification as molecular features become clearer.

Small Cell Lung Cancer

Small cell lung cancer (SCLC) is a high-grade neuroendocrine carcinoma. Neuroendocrine cells receive and release chemical signals that help regulate body functions.

Small cell lung cancer accounts for about 10% to 15% of lung cancers. Of the two main types of lung cancer, SCLC usually grows and spreads more quickly. It often begins near the large central airways, can spread quickly and often recurs after treatment. It has a strong association with tobacco exposure.
 

Small Cell Carcinoma

Small cell carcinoma is the most common form of SCLC. It is sometimes called oat cell carcinoma because of how the cells may appear under a microscope.

This name describes the cancer cells, not the tumour’s size. A large tumour can consist of small cancer cells, while a small lung tumour can contain another cancer type.
 

Combined Small Cell Lung Carcinoma

Combined small cell lung carcinoma contains an area of small cell carcinoma together with a component of non-small cell lung cancer (NSCLC), such as adenocarcinoma or squamous cell carcinoma. It is a rare type of lung cancer.

Identifying both components is important because the combined features may influence treatment decisions and the treatment plan. The lung cancer diagnosis sometimes becomes clear only after a larger tissue sample is examined.

Other Neuroendocrine Tumours of the Lung

Not every neuroendocrine tumour in the lung is small cell lung cancer. Other pulmonary neuroendocrine tumours include:

• Typical carcinoid tumour
• Atypical carcinoid tumour
• Large cell neuroendocrine carcinoma

Typical and atypical lung carcinoid tumours often grow more slowly than high-grade neuroendocrine carcinomas. Large cell neuroendocrine carcinoma is a rare, high-grade cancer that may behave more aggressively.

These tumours belong to the broad group of pulmonary neuroendocrine neoplasms. However, their pathological features, grade, behaviour and treatment may differ considerably.

Primary Lung Cancer and Secondary Cancer in the Lungs

Primary lung cancer begins in lung tissue. Secondary cancer in the lungs begins in another organ and later spreads to the lungs. This distinction identifies where the cancer started.

For example, breast or colorectal cancer that spreads to the lungs remains breast or colorectal cancer. It does not become a new primary lung cancer because the cancer started outside the lung. These secondary tumours are not types of lung cancer. Learn more about cancer that has spread to the lungs.

Mesothelioma is also not a type of lung cancer. It usually begins in the pleura, the thin tissue covering the lungs and lining the chest wall.

How Is the Lung Cancer Type Confirmed?

Imaging can show the location and size of a lung lesion, but it usually cannot identify the cancer type. Distinguishing the types of lung cancer generally requires a biopsy.

A pathologist examines the lung tissue under a microscope. Special laboratory stains, called immunohistochemistry, can identify proteins associated with particular cell types and separate one cancer type from another.

A small sample may sometimes be reported as “non-small cell lung cancer, not otherwise specified” or “NSCLC-NOS”. This means the sample confirms non-small cell lung cancer but does not contain enough information for a more specific classification. Further testing or a larger sample may clarify the subtype.

Molecular testing provides additional information about gene changes within the cancer cells. A biomarker does not replace the histological diagnosis. For example, an EGFR-positive adenocarcinoma remains an adenocarcinoma.

Read more about biopsies, pathology and biomarker testing in the guide to lung cancer diagnosis and treatment.

Why the Lung Cancer Type Matters

The cancer type helps the healthcare team understand how the tumour may behave and which treatment options may be appropriate. The types of lung cancer respond differently to treatment, so type can affect treatment decisions and the treatment plan.

Treatment approaches differ between non-small cell lung cancer and small cell lung cancer. Chemotherapy forms the basis of care for most SCLC and may be combined with radiotherapy or immunotherapy. NSCLC treatment options, including targeted therapy for some cancers, depend on many factors:

• The stage of the lung cancer
• The cancer subtype and tumour biomarkers
• Whether the cancer can be removed completely
• Lung function and overall health
• Previous treatment
• The person’s preferences and treatment goals

Surgery is more commonly considered for selected localised non-small cell lung cancer. It has a limited role in small cell lung cancer and is usually considered only in uncommon, early-stage lung cancer after careful staging. Detailed information about eligibility, procedures and recovery belongs in the guide to lung cancer surgery.

Thoracic Surgical Assessment at Neumark

Neumark Lung and Chest Surgery Centre specialises in minimally invasive thoracic surgery with a multidisciplinary approach led by Dr Harish Mithiran, senior consultant thoracic surgeon at Gleneagles and Mount Alvernia hospitals.

A thoracic surgical assessment may be appropriate when imaging shows a suspicious lung tumour, a biopsy confirms potentially operable lung cancer, or the treating team recommends reviewing surgical options. Patients can contact Neumark to discuss an appropriate assessment.