Cancers are classified in two ways: by the type of tissue
in which the cancer originates (histological type) and by
primary site, or the location in the body where the cancer
first developed. This section introduces you to the first
method: cancer classification based on histological type.
The international standard for the classification and nomenclature
of histologies is the International Classification of Diseases
for Oncology, Third Edition (ICD-O-3). Click here
to go to the ICD-O-3 training module.
From a histological standpoint there are hundreds of different
cancers, which are grouped into five major categories: carcinoma,
sarcoma, myeloma,
leukemia, and lymphoma.
In addition, there are also some cancers of mixed
types.
Carcinoma
Carcinoma refers to a malignant neoplasm of epithelial origin
or cancer of the internal or external lining of the body.
Carcinomas, malignancies of epithelial tissue, account for
80 to 90 percent of all cancer cases.
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Epithelial tissue is found throughout
the body. It is present in the skin, as well as the
covering and lining of organs and internal passageways,
such as the gastrointestinal tract.
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Carcinomas are divided into two major subtypes: adenocarcinoma,
which develops in an organ or gland, and squamous cell carcinoma,
which originates in the squamous epithelium.
Adenocarcinomas generally occur in mucus membranes and are
first seen as a thickened plaque-like white mucosa. They often
spread easily through the soft tissue where they occur. Squamous
cell carcinomas occur in many areas of the body.
Most carcinomas affect organs or glands capable of secretion,
such as the breasts, which produce milk, or the lungs, which
secrete mucus, or colon or prostate or bladder.
Sarcoma
Sarcoma refers to cancer that originates in supportive
and connective tissues such as bones, tendons, cartilage,
muscle, and fat. Generally occurring in young adults,
the most common sarcoma often develops as a painful
mass on the bone. Sarcoma tumors usually resemble
the tissue in which they grow.
Examples of sarcomas are:
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- Osteosarcoma or osteogenic sarcoma (bone)
- Chondrosarcoma (cartilage)
- Leiomyosarcoma (smooth muscle)
- Rhabdomyosarcoma (skeletal muscle)
- Mesothelial sarcoma or mesothelioma (membranous lining
of body cavities)
- Fibrosarcoma (fibrous tissue)
- Angiosarcoma or hemangioendothelioma (blood vessels)
- Liposarcoma (adipose tissue)
- Glioma or astrocytoma (neurogenic connective tissue found
in the brain)
- Myxosarcoma (primitive embryonic connective tissue)
- Mesenchymous or mixed mesodermal tumor (mixed connective
tissue types)
Myeloma
Myeloma is cancer that originates in the plasma cells of
bone marrow. The plasma cells produce some of the proteins
found in blood.
Leukemia
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Leukemias ("liquid cancers"
or "blood cancers") are cancers of the bone
marrow (the site of blood cell production). The word
leukemia means "white blood" in Greek. The disease is
often associated with the overproduction of immature
white blood cells. These immature white blood cells
do not perform as well as they should, therefore the
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patient is often prone to infection. Leukemia also affects red
blood cells and can cause poor blood clotting and fatigue due
to anemia. Examples of leukemia include:
- Myelogenous or granulocytic leukemia (malignancy of the
myeloid and granulocytic white blood cell series)
- Lymphatic, lymphocytic, or lymphoblastic leukemia (malignancy
of the lymphoid and lymphocytic blood cell series)
- Polycythemia vera or erythremia (malignancy of various
blood cell products, but with red cells predominating)
Lymphoma
Lymphomas develop in the glands or nodes of the lymphatic
system, a network of vessels, nodes, and organs (specifically
the spleen, tonsils, and thymus) that purify bodily fluids
and produce infection-fighting white blood cells, or lymphocytes.
Unlike the leukemias which are sometimes called "liquid
cancers," lymphomas are "solid cancers." Lymphomas
may also occur in specific organs such as the stomach, breast
or brain. These lymphomas are referred to as extranodal lymphomas.
The lymphomas are subclassified into two categories:
Hodgkin lymphoma and Non-Hodgkin lymphoma. The presence
of Reed-Sternberg cells in Hodgkin lymphoma diagnostically
distinguishes Hodgkin lymphoma from Non-Hodgkin lymphoma.
Mixed Types
The type components may be within one category or from different
categories. Some examples are:
- adenosquamous carcinoma
- mixed mesodermal tumor
- carcinosarcoma
- teratocarcinoma
In the next section, you will be provided with a comprehensive
list of tissue types and the tumors that arise from them.
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