The question is, "What is Cancer?"  Now we Know.

What is cancer?  It's the fourth position in the zodiac and the name "cancer" comes from the Latin word for crab.  From the Greek language, we get "metastasis" for a "change in position".  The Latin "cancer" and the Greek "metastasis" both describe how the disease cancer moves. 

It moves in a crab-like fashion to invade healthy tissue and then Metastasizes to move from its primary site to tissues or organs some distance from where it started.

Photo:  The Crab Nebula in the Taurus constellation is a good depiction of how cancer invades surrounding tissue.

Crab nebula from NASA/ESA.  Created for NASA by SCScl under contract NAS5-26555 What is cancer? It's good cells gone bad. Remember our friends the vampires? As long as they can get human blood, they never die. Cancer cells are the same way. As long as they have a good blood supply, they are immortal.

Let's back up and review a couple of things about cells.
Human cells have a nucleus that houses DNA which is what carries the genetic blueprints of all life forms.  It's the information contained in the DNA that guides the construction and functioning of all living things.

DNA is very delicate and can be damaged by a large number of things, mostly environmental but some biologic as well.

If a cell carrying damaged DNA isn't detected and destroyed by the protective mechanisms in our body, that cell will replicate and create a mutated version of itself.  Thus we have the foundation of evolution.

The downside is that the damaged or changed cell can cause cancer. 

Back to the root question...what is cancer?  For a good read on the subject that will answer that question, consider the book, "How Cancer Works". Just click on the link below to for more information on ordering this informative book.

How Cancer Works

Stem Cells and Differentiation

To address the original question of "what is cancer", we need to consider how stem cells change to their final form, a process called "differentiation". 

We hear a lot about stem cells these days and it's a hot area of research, also one charged with all kinds of political, religious and ethical arguments; most of which arise from a woeful lack of understanding about stem cells.

Thus, this seems like a good a place as any to introduce, What Science Knows About Cancer, a timely DVD course offering from the Great Courses.  Click on the Great Courses button below to see this amazing course.  Just enter the course name in the Great Courses search box when it appears.

We have a storehouse of stem cells throughout our body and they function to repair and replace injured tissue throughout our whole lifespan.  The wonderfully intriguing thing about stem cells is that they have the ability to become any type of cell the body requires. 

Embryonic stem cells start out as totipotent, meaning that they can become any type of cell.  On their way to becoming that final cell form, they travel through several stages in which they increasingly lose that ability.

The stages are totipotent, pluripotent, multipotent, committed, determined, and fully differentiated then terminally differentiated (unipotent). 

The diagram below shows a fertilized egg (oocyte + sperm) becoming a totipotent morula (early stage embryo of 16 to 32 cells), growing to a blastocyst where pluripotent inner mass cells are produced, which ultimately become a heart, neuron, immune cell or whatever they are directed to become.

Original work by author Mike Jones for Wikipedia, May 3, 2006.  This file is licensed under the Creative Commons Attribution shareAlike 2.5 License.

The whole journey is called the differentiation cascade and that last stop, terminally differentiated, is where the cell finally becomes what its DNA has instructed it to become.  A lot of cell divisions have occurred by the time a cell reaches full or terminal differentiation.

Back to the Basic Question...
"What is Cancer?"

We needed a discussion on differentiation because the first and most important thing about cancer is that the stem cells fail to differentiate somewhere along the cascade. 

They divide and divide but never progress to a final destination.  What is Cancer?  Uncontrolled growth is another clue to the answer. 

As we can imagine, all that division with no place to go, results in a clumping together of cells that we call a tumor.

Here is an incredible 9 minute video from YouTube narrated by Thea Tlsty of the Comprehensive Cancer Center at the University of California, San Francisco.  It has a wealth of microscopic imaging of "cancer cells behaving badly"...highly graphic, informative and worth watching.


If the tumor stayed put and just grew, we could deal with it fairly easily at some point but...another bad thing about cancer is that it has the potential to invade surrounding tissue.

As long as the cancer stays in place, in situ as it's called, no metastasis has taken place.  This is where the crab name
came from; it invades surrounding tissue in crab-like movements.


Metastasis takes us one step further in the "what is cancer" question.  It's a fine point, but what is meant here is the "potential" to metastasize. 

Invasion of surrounding tissue has to occur before the cancer is primed to metastasize, meaning "change its position" to some distant locale.  It moves out of the confining tissue and is transported by the blood stream, lymphatic system or direct transmission to some other point where it continues its unchecked growth.

One thing that makes cancer so fearsome is that it is potentially fatal in that sooner or later it will end up in a vital organ and grow to the point of organ failure causing death.

Photo left:  Liver slice showing multiple metastatic nodules originating from primary pancreatic cancer.

Cut surface of liver showing multiple metastatic nodules originating from pancreatic cancer, author Haymanj, 2002

For example, breast cancer is not fatal since the breast is not a vital organ but when it metastasizes to the liver or lungs, then we have the potential fatality. 

Cancer is lethal by design in that the strongest, fittest, most aggressive cancer cells live while the weaker ones are taken care of by our immune system.

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Another thing about cancer is that it is immortal.  Normal cells have a programmed life span, die and are replaced.

Cancer cells never get the signal that it's time to die.  As long as they can get fed from a good blood supply, they live on and on. 

Caller ID

This takes us to another characteristic of cancer.  Cancer cells do not respond to outside signals at all.  They only pay attention to their own autonomous signals which means that they are not responsive to the "braking" signals that would slow or stop the division of normal cells. 

In a sense, cancer cells have caller ID.  When they see the "call" to die coming in, they just don't answer.  

Think of driving your car down the highway going faster and faster and discovering that the accelerator is stuck.  Now you hit the brakes only to find out that the brakes have failed.  That's a pretty good analogy to the question, "what is cancer?".

Follow the link to the next page to delve into what causes cancer.

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