Non-small cell lung cancer is the most common type of lung cancer, diagnosed in 85 to 90% of lung cancer cases. There are several subtypes of non-small cell lung cancer1:
About 25% to 30% of all lung cancers are squamous cell carcinomas. These cancers start in early versions of squamous cells, which are flat cells that line the inside of the airways in the lungs. They are often linked to a history of smoking and tend to be found in the middle of the lungs, near a bronchus.
About 40% of lung cancers are adenocarcinomas. These cancers start in early versions of the cells that would normally secrete substances such as mucus. This type of lung cancer occurs mainly in current or former smokers, but it is also the most common type of lung cancer seen in non-smokers. It is more common in women than in men, and it is more likely to occur in younger people than other types of lung cancer.
Adenocarcinoma is usually found in outer parts of the lung. It tends to grow slower than other types of lung cancer, and is more likely to be found before it has spread outside of the lung.
People with a type of adenocarcinoma called adenocarcinoma in situ (previously called bronchioloalveolar carcinoma) tend to have a better outlook (prognosis) than those with other types of lung cancer.
This type of cancer accounts for about 10% to 15% of lung cancers. It can appear in any part of the lung. It tends to grow and spread quickly, which can make it harder to treat. A subtype of large cell carcinoma, known as large cell neuroendocrine carcinoma, is a fast-growing cancer that is very similar to small cell lung cancer.
There are also a few other subtypes of non-small cell lung cancer, such as adenosquamous carcinoma and sarcomatoid carcinoma. These are much less common.
Stages of non-small cell lung cancer
Treatment and prognosis are based on the stage of cancer, which is how far it has spread. There are two types of stages for non-small cell lung cancer (NSCLC)2:
- Clinical - Based on the results of the physical exam, biopsies, and imaging tests (CT scan, chest x-ray, PET scan, bone scan).
- Pathologic – Clinical stage factors plus results of surgery, which may reveal cancer in other places.
TNM staging system
The American Joint Committee on Cancer (AJCC) uses the TNM staging system3, which is based on three key pieces of information:
- T - Refers to size, extent or penetration of the main tumor.
- N - Refers to node, including how many nearby nodes have cancer and their location.
- M - Refers to distant metastasis, or spread of cancer cells outside the local tumor.
Numbers are assigned to each of the T, N and M categories to indicate severity and then the information is combined to assign an overall stage of I, II, III or IV of lung cancer. This process is called stage grouping. Stage I is early-stage cancer and stage IV cancer is advanced (has usually spread to other parts of the body)4. Patients with lower-number stages tend to have a better outlook2.
- Occult (hidden cancer) - Tumor cells found in sputum, but not in imaging tests.
- Stage 0 - Abnormal cells found only in the innermost lining of the lung, also referred to as "carcinoma in situ" that is non-invasive.
- Stage IA/B - Invasive cancer that has grown deeper into lung tissue, but has not invaded nearby tissues or lymph nodes. Tumor is 5 cm wide or less.
- Stage IIA/B - Tumor is less than 7 cm wide, and cancer cells are found in nearby lymph nodes or tissues, such as chest walls. May be multiple tumors.
- Stage IIIA/B - Tumor may be any size and there may be multiple malignant tumors in the lung. Cancer cells may have invaded lymph nodes in chest/neck and tumor may have invaded nearby organs such as esophagus or heart.
- Stage IV - Malignant tumors in both lungs. Or, cancer may have spread to other parts of the body, such as bones, brain or liver, or in fluid between the pleura layers in the lungs.