Lung cancers, also known as bronchogenic carcinomas ("carcinoma" is another term for cancer), are broadly classified into two types: small cell lung cancers (SCLC) and non-small cell lung cancers (NSCLC). This classification is based upon the microscopic appearance of the tumor cells. These two types of cancers grow, spread, and are treated in different ways, so a distinction between these two types is important.
SCLC comprises about 10%-15% of lung cancers. This type of lung cancer is the most aggressive and rapidly growing of all the types. SCLC is strongly related to cigarette smoking with only 1% of these tumors occurring in non-smokers. SCLCs metastasize rapidly to many sites within the body and are most often discovered after they have spread extensively.
In its early stages, lung cancer normally has no symptoms. When symptoms start to appear, they are usually caused by blocked breathing passages or the spread of cancer further into the lung, surrounding structures, other parts of the body.
Lung cancer symptoms may include:
Chronic, hacking, raspy coughing, sometimes with blood-streaked mucus
Recurring respiratory infections, including bronchitis or pneumonia
Increasing shortness of breath, wheezing, persistent chest pain
NSCLC is the most common lung cancer, accounting for about 85%-90% of all cases. NSCLC has three main types designated by the type of cells found in the tumor. They are:
Adenocarcinomas are the most common type of NSCLC in the U.S. and comprise up to 40% of NSCLC cases. While adenocarcinomas are associated with smoking like other lung cancers, this type is also seen in non-smokers -- especially women -- who develop lung cancer. Most adenocarcinomas arise in the outer, or peripheral, areas of the lungs. They also have a tendency to spread to the lymph nodes and beyond. Bronchioloalveolar carcinoma is a subtype of adenocarcinoma that frequently develops at multiple sites in the lungs and spreads along the preexisting alveolar walls. It may also look like pneumonia on a chest X-ray. It is increasing in frequency and is very common in non-smoking women and in the Asian population.
Squamous cell carcinomas were formerly more common than adenocarcinomas; at present they account for about about 25% of NSCLC cases. Also known as epidermoid carcinomas, squamous cell cancers arise most frequently in the central chest area in the bronchi. This type of lung cancer most often stays within the lung, spreads to lymph nodes, and grows quite large, forming a cavity.
Large cell carcinomas, sometimes referred to as undifferentiated carcinomas, are the least common type of NSCLC, accounting for 10%-15% of all lung cancers. This type of cancer has a high tendency to spread to the lymph nodes and distant sites.