The Five Broad Categories of Cancer

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It is much easier to understand what it means to have bone cancer than what it means to have Ewing sarcoma. The same is true for pancreatic cancer versus pancreatic adenocarcinoma. Nonetheless, we come across these cancer terms that typically end in –oma that can be very confusing.

Actually, it's not simply that they can be very confusing, they in fact are extremely confusing. They sometimes combine or contradict or get used in ways that seem like the reading equivalent of medieval torture.

Categories

The National Cancer Institute recognizes five broad categories of cancer types.

Before looking more closely at each category, it is important to remember that these terms apply in the case of a primary cancer site. In other words, they refer to the place of origin of the cancer. They don't refer to a cancer that has spread from elsewhere in the body to become a secondary site. For instance, a central nervous system cancer is one that begins in those cells, while central nervous system lymphoma is a cancer that began in lymphatic tissue and spread to the central nervous system.

SARCOMA

Sarcomas form in what are called mesenchymal cells, cells that make up connective or supportive tissue, including cartilage, bone, fat, muscle, fibrous tissue, and blood vessels, among others

Therefore a sarcoma is a malignant cancer of mesenchymal cells. In humans, sarcomas are extremely rare.

Examples:

  • Rhabdomyosarcoma—cancer that forms in muscle
  • Osteosarcoma—cancer that forms in bone
  • Liposarcoma—cancer that forms in fat tissue
  • Gastrointestinal stromal tumor (GIST)

CARCINOMA

Carcinomas begin in skin or in tissue that line or cover internal organs. The majority of cancers are carcinomas.

Here, it is important to note the subtype adenocarcinoma. An adenocarcinoma is a cancer that begins in cells that secrete substances (glandular cells). These substances include mucus and digestive fluids. Most of the cancers that are classified as breast, colon, pancreas, lung and prostate cancers are adenocarcinomas.

Examples:
Breast cancer—most often, breast cancers are mammary ductal adenocarcinomas, including:

  • Invasive ductal carcinoma
  • Invasive lobular carcinoma
  • Ductal carcinoma in situ

Colon cancer—most colon cancers are adenocarcinomas of the colon.

  • Mucinous adenocarcinoma
  • Signet ring adenocarcinoma

Lung cancer—technically it's called a pulmonary carcinoma, or a carcinoma of the lung, and the main subtypes are small-cell lung carcinoma and non-small cell lung carcinoma. The latter has three main subtypes of its own:

  • Adenocarcinoma of the lung
  • Squamous-cell carcinoma of the lung
  • Large-cell carcinoma of the lung

Pancreatic cancer—far and away the most common form is adenocarcinoma of the pancreas.

LEUKEMIA

Leukemia is sometimes called a 'liquid cancer' because unlike virtually all other cancer types, in leukemia the patient does not develop any solid tumors. The cancer is confined to unattached cancerous cells in the blood and bone marrow.

When understanding a leukemia, the keys are found in the first two modifiers used: acute or chronic, and lymphocytic or myeloid.

Examples:

  • Acute lymphocytic leukemia
  • Chronic myeloid leukemia

If a leukemia is 'acute' it is an aggressive cancer. If chronic, it is indolent (slow-growing).

If it is lymphocytic, it affects lymphoid cells. Another term often used is lymphoblastic.

If it is myeloid, it affects myeloid cells. Other terms used include myelogenous and myeloblastic. Don't be confused, they refer to the same thing. Why they can't decide to use only one is a mystery.

Click here for a closer look at leukemia.

LYMPHOMA and MYELOMA

These are cancers that form in lymphatic tissue or (in myeloma) in plasma cells and that affect the immune system. While both lymphoma and leukemia are regarded as "lymphoid cancers" and "blood cancers" the chief difference is that in lymphoma, tumors can develop, or, if not traditional tumors, then at least clusters of cancerous cells (found in lymph nodes, for instance; or in bulky masses).

Examples:

  • Hodgkin's lymphoma
  • Diffuse large B-cell lymphoma
  • Peripheral T-cell lymphoma
  • Multiple Myeloma

CNS CANCERS

A central nervous system cancer is just that—a cancer that develops from the cells of the brain or spinal cord. About the only good thing about these cancers is that they rarely ever spread to other parts of the body. This fact does not prevent them from being life-threatening.

Examples:
Glioma—a cancer that begins in glial cells. Since there are several types of glial cells, they have their own names:

  • Astrocytoma—a cancer that begins in a type of glial cells known as astrocytes.
  • Glioblastoma multiforme—a cancer that also begins in astrocytes. In fact, this is simply another name for a high grade (aggressive) astrocytoma. Sometimes it seems like they're confusing us on purpose, doesn’t it?
  • Oligodendroglioma—a slow-growing cancer that begins in glial cells known as oligodendrocytes.

Now that you have a general understanding of the five categories of cancer types, expect to come across a term that somehow doesn't fit into any of the categories. It's maddening!

Sources:
National Cancer Institute
American Cancer Society
American Joint Committee on Cancer

Photo by WoodleyWonderWorks

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