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Metastasis: How Cancer Spreads

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  • 0:06 Spread around the Body
  • 0:38 Metastasis
  • 1:44 Angiogenesis
  • 3:48 Where Cancer Cells Spread
  • 6:41 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
This lesson will describe the concept of cancer spreading around the body, or metastasis, as well as why it may occur, how it occurs, why it may fail, and how your blood vessels play a critical role in this process.

Spread Around the Body

When we travel to our most favorite destinations, be it Aruba, Jamaica, Bermuda, or the Bahamas, as long as there's a beach, we'll probably be happy. How we get there is another story. We may have to drive along a road from our home to the airport or seaport and from there travel via specialized air channels or sea lanes to get to where we want to go. Along our journey, we face the dangers of crashes and other things. This analogy is similar to how some very bad cells may spread around your body.

Metastasis

I wouldn't be surprised, whether from another lesson or from your own education, if you've heard of the very important term metastasis, which is the spread of cancer cells around the body. Everyone uses this term left and right, but few people can explain how it begins or why it may occur. Frankly, even scientists don't fully understand the answers to those questions, but at minimum, I'll tell you about the fundamental answers to these questions.

First of all, a cell doesn't become cancerous over nothing. No! There's a reason. There's a whole sequence of events of a normal and healthy cell becoming cancerous. Actually, it's usually quite difficult for a normal cell to become malignant, let alone survive for long.

The details of why this occurs were discussed in the lesson that went over the initiation, promotion, and progression of cancer. In summary, these steps cause a cell to mutate, then multiply, and finally invade surrounding tissues and spread around the body, respectively. In order for this spread to occur something important must happen first.

Angiogenesis

You see, a collection of cancerous cells, known together as a malignant tumor, can only grow so large at first. That's because when you grow bigger and bigger as you go from infant to toddler to teen and beyond, you need an increasing amount of nutrients to do so. That's why people who grow up in very poor or war-torn conditions are often small in stature; it's because they didn't get enough nutrients while growing up.

Similarly, if a tumor wants to grow bigger and start spreading around, it needs more and more nutrients as it grows. To get these critical nutrients, it must establish a connection to one thing that carries these vital nutrients around your body. It's called the vasculature, or your blood vessels. Just like parasites that like to leech off of your blood for nutrition, so, too, do tumors leech off of your life-giving force to eventually kill you.

The process by which new blood vessels form or sprout from existing ones in order to connect to the tumor is called angiogenesis, or tumor angiogenesis in our specific cause for new blood vessel formation. The tumor secretes all sorts of chemicals, including VEGF, or vascular endothelial growth factor, that tell the body to start growing branches and tentacles off of existing blood vessels directly to the tumor. Once this connection is established, the tumor can grow like crazy.

Just as an interesting side-note, a tumor can grow so fast and large thereafter that it may actually outgrow and outstrip its own blood supply. If this happens, the tumor cells obviously begin to die, leading to the formation of very soft, fluid, and often pus-filled necrotic areas sometimes found in late stages of certain cancers.

Where Cancer Cells Spread

But, I digress. After the new connection to your body's vasculature is established, the cancer cells use the mutations they underwent during their development to their advantage. These mutations allow a cancer cell to basically unstick itself from its surrounding area, something normal cells cannot do, and begin to move towards the blood vessels or lymphatic vessels and force these vessel walls open - and therefore gain entry into your vasculature.

Once inside of your blood vessels, the cancer cells aren't home free. These blood vessels are like the roads or sea lanes you use to travel to your destination. Before you can get to your destination, you must endure slick roads, other cars trying to run you off the road, icebergs (okay, maybe not in the Caribbean) - you get the point.

Similarly speaking, most cancer cells that enter the blood vessels die. Most cancer cells do not complete their journey to their vacation spot. This occurs for many reasons, including the fact that some of them:

  • Cannot handle the environmental, or chemical, changes in the vasculature and end up bursting open.
  • Bump violently against vessel walls and are killed that way, kind of like a car crash.
  • Are destroyed by your immune system that's on the lookout for these dangerous cells, sort of like cops may have to shoot a dangerous prison escapee.

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