Non-small cell lung cancer (NSCLC) is the most commonly diagnosed type of primary lung cancer — meaning cancer that originated in the lungs. NSCLC makes up from 80 to 85 percent of lung cancer diagnoses, with small cell lung cancer (SCLC) comprisings only 10 to 15 percent of diagnoses. It is important to determine the type of lung cancer a patient has, as this will affect what treatments should be considered.
The type of lung cancer is generally determined by observation under the microscope, as the cells making up NSCLC tumors are larger than those making up SCLC.
Types of NSCLC
A diagnosis of NSCLC can cover a range of tumor types that tend to behave similarly and have similar reactions to treatment. A single tumor can consist of multiple types of NSCLC cells. NSCLC tends to be divided into three categories: adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. However, it is possible that if the cancer is in the very early stages, a complete diagnosis cannot be made.
Adenocarcinoma is the most common type of lung cancer (making up around 40 percent of diagnoses) and is the most frequent lung cancer found in non-smokers. This type of lung cancer is slightly more common in women than men, and tends to be diagnosed in younger patients.
Adenocarcinoma develops in the early versions of mucus-producing cells in smaller airways, like bronchioles, found toward of edges of the lungs. It tends to grow and spread very slowly compared to other types of lung cancer, which often allows for early diagnosis.
Squamous cell carcinoma
Squamous cell carcinoma is the second most common type, accounting for around 30 percent of lung cancer diagnoses. It is the NSCLC most associated with smoking, although other factors (such as asbestos and age) can also play a role.
Squamous cell tumors develop in the thin, flat “squamous” cells that line the airways. These squamous cells are also found on the skin and lining of other organs, and for this reason is also be referred to as epidermoid carcinoma. Squamous cell tumors tend to develop in the central part of the lungs or the main airways (the primary bronchi), and can spread to other parts of the body.
Large cell carcinoma
Large cell carcinomas do not have a common site of origin and are defined by the large size of these cells compared to that of SCLC cells. With improved diagnostic technique, the number of tumors classified as large cell carcinomas is declining, as doctors more accurately observe cells and pinpoint the origin of the cancer, enabling better treatment. Large cell carcinomas are more common in men than women.
Another variant of large cell carcinoma is termed large cell neuroendocrine carcinoma (LCNEC). This type is very rare, making up about 3 percent of all diagnoses, and tends to be more common in smokers and men. Although rare, it is thought to be the fastest growing type of NSCLC.
Staging of NSCLC
In general, NSCLC spreads much slower than SCLC, making it easier to determine how far the cancer has progressed (the stage) and correctly tailor treatment based on this. NSCLC has four defined stages based on its growth and progression, and this can affect the prognosis of the cancer.
At stage 1, the cancer is only present in the lung and is smaller than 5 cm (2 inches) in area. At stage 2, NSCLC has either spread to nearby lung structures and lymph nodes or has grown beyond 5 cm. At stage 3, the tumor has either grown considerably and invaded other organs near the lungs, or has spread to distant lymph nodes in the body. A stage 4 cancer has spread beyond the initially affected lung to nearby organs and more distant parts of the body.
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