Types
of lung cancer
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 themselves. These two types
of cancers grow and spread in different ways, so a distinction between these two
types is important.
SCLC comprise about 20% of lung cancers and are the most aggressive and rapidly
growing of all lung cancers. SCLC are strongly related to cigarette smoking with
only 1% of these tumors occurring in non-smokers. SCLC metastasize rapidly to
many sites within the body and are most often discovered after they have spread
extensively. Referring to a specific cell type often seen in SCLC, these cancers
are sometimes called oat cell carcinomas.
NSCLC are the most common lung cancers, accounting for about 80% of all lung
cancers. NSCLC has three main types that are named based upon the type of cells
found in the tumor. They are:
- Adenocarcinomas are the
most commonly seen type of NSCLC in the U.S. and comprise up to 50% of NSCLC .
While adenocarcinomas are associated with smoking like other lung cancers,
this type is especially observed as well in non-smokers who develop lung
cancer. Most adenocarcinomas arise in the outer, or peripheral, areas of the
lungs. Bronchioloalveolar carcinoma is a subtype of adenocarcinoma that
frequently develops at multiple sites in the lungs and spreads along the
preexisting alveolar walls.
- Squamous cell carcinomas
were formerly more common than adenocarcinomas; at present they account for
about 30% of NSCLC. Also known as epidermoid carcinomas, squamous cell cancers
arise most frequently in the central chest area in the bronchi.
- Large cell carcinomas,
sometimes referred to as undifferentiated carcinomas, are the least common
type of NSCLC.
- Mixtures of different types of NSCLC are also seen.
Other types of cancers can arise in the lung; these types are much less common
than NSCLC and SCLC and together comprise only 5-10% of lung cancers:
- Bronchial carcinoids
account for up to 5% of lung cancers. These tumors are generally small (3-4 cm
or less) when diagnosed and occur most commonly in persons under 40 years of
age. Unrelated to cigarette smoking, carcinoid tumors can metastasize, and a
small proportion of these tumors secrete hormone-like substances. Carcinoids
generally grow and spread more slowly than bronchogenic cancers, and many are
detected early enough to be amenable to surgical resection.
- Cancers of supporting lung tissue such as smooth muscle, blood vessels, or
cells
involved in the immune response can rarely occur in the lung.
As discussed previously, metastastatic cancers from other primary tumors in the
body are often found in the lung. Tumors from anywhere in the body may spread to
the lungs either through the bloodstream, through the lymphatic system, or
directly from nearby organs. Metastatic tumors are most often multiple,
scattered throughout the lung and concentrated in the peripheral rather than
central areas of the organ.
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