Eli5; How does cancer kill you?

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My mother died of bowel cancer when I was a teenager, it has spread to her bladder, lungs and liver. I still wonder how it actually killed her. What went wrong that stopped her heart pumping and lungs breathing?

In: Biology

Cancer are unregulated cells that don’t follow their original function. This is often characterized by uncontrolled cell division, creating a tumor, or a clump of cells.

Now tumors can inhibit function several ways, the most common being applied pressure or waste products that can be bad for healthy cells.

Many cancers aren’t particularly dangerous where they originate, but instead where they end up. Think breast and testicular cancer. While you might lose function of those organs, they aren’t strictly necessary for survival.

The problem occurs when they break off (metastasis) and migrate to other parts of the body that are vital and inhibit their function. Think brain, heart, lungs. Many of those locations have specific functions and large tumors or bi-products of cancer cells can mess that up.

Edit- As u/Tdshimo said, resource stealing is another big reason why tumors hurt a localized area.

Cancer kills by interfering with the normal, necessary function of organs and bodily processes, whether directly – by invading the organ tissue, or by crowding it out, or indirectly by growing so large it steals blood flow from necessary tissues.

Cancer is basically a single word humans use to describe any clump of cells that (for a large variety of different reasons) decide to go rogue and start multiplying instead of doing the jobs they are usually supposed to do to keep us alive.

Sometimes, if the clump of cells (which gets called a “tumor”) is small enough and all in one place, doctors are able to simply cut it out with surgery. Other times, we’ll try to use drugs (chemotherapy) or radiation to basically carpet-bomb everything around the cancer, with the hope that our remaining good cells can rebuild afterwards.

Unfortunately, that carpet-bombing isn’t always effective, because if we completely nuke everything we wont have enough surviving good cells to rebuild, but if too many rogue cells survived they can just go on rebuilding tumors instead.

When some of these rogue cells start setting up shop in a place like the liver or kidneys it can be trouble. It’s different from say a heart attack, or stopping breathing, but we still absolutely need our kidneys and liver to function properly to filter out the waste products our own body naturally produces. If rogue cells hijack too many resources (like food, air, etc.) from our good cells so that our good cells no longer have enough energy to keep up with filtering out or processing all those waste products, then those waste products will start to accumulate in our blood stream and those waste products will end up basically poisoning everything. That poisoning is what can eventually cause our heart or lungs or brain to fail.

Sorry to hear of your loss, it horrible to lose a parent in this way.

My father passed away “from” bowl cancer Jan this year…
It was the morphine actually killed him (it was a sweat relief).
He had a full obstruction of the bowl and was in a lot of pain, the morphine wasn’t really touching it, the doc who came to the house (he wanted to die at home) audibly noted that the new stat dose he was administering was “at the upper limits of a non lethal dose”… after the dose, he sort of went calm, then into a sleep and passed away…we was all by his side…the doc was visibly shaken, he knew what had happened, I shock his hand and thanked him, dad had suffered enough.

Cancer such a horrible disease 😞

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What is colon or rectum cancer?

Cancer can start any place in the body. Cancer that starts in the colon or rectum is often called [colorectal cancer](https://www.cancer.org/cancer/colon-rectal-cancer/about/what-is-colorectal-cancer.html). It starts when cells in the colon or rectum grow out of control and crowd out normal cells. This makes it hard for the body to work the way it should.

Cancer cells can spread to other parts of the body. Cancer cells in the colon or rectum can sometimes travel to the liver and grow there. When cancer cells do this, it’s called metastasis (pronounced meh-TAS-tuh-sis). To doctors, the cancer cells in the new place look just like the ones from the colon or rectum.

Cancer is always named for the place where it starts. So when colorectal cancer spreads to the liver (or any other place), it’s still called colorectal cancer. It’s not called liver cancer unless it starts from cells in the liver.

## The colon and rectum

Colon cancer starts in the colon, and rectal cancer starts in the rectum. These are both part of the digestive system. This is where food is broken down to make energy and where the body gets rid of solid waste (poop or stool).

In most cases, colon and rectal cancers grow slowly over many years. We now know that most of those cancers start as a growth called a polyp. Taking out the polyp early may keep it from turning into cancer.

## Are there different kinds of colon and rectum cancers?

There are [a few kinds of colon and rectum cancers](https://www.cancer.org/cancer/colon-rectal-cancer/about/what-is-colorectal-cancer.html). Your doctor can tell you more about the kind you have. 

The most common kind is called adenocarcinoma (AD-uh-no-KAR-sin-O-muh). This kind starts in the cells that make mucus to cover the inside surfaces of the colon and rectum.

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## [https://www.cancer.org/cancer/colon-rectal-cancer/if-you-have-colon-rectal-cancer.html](https://www.cancer.org/cancer/colon-rectal-cancer/if-you-have-colon-rectal-cancer.html)

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Cancer is basically a cell that does not die, but instead keeps on multiplying AND the copies can travel through bodily fluids to different locations.

Death may finally occur by many mechanisms; here are a few…

* The cancer cells steal resources and suppress appetite making the patient severely malnourished. The sheer loss of body mass can itself be fatal.
* Their muscles waste away till they cannot move even breathe or cough properly. Some may die of lung infections or choke on food.
* The cancer or one of its deposits may eat through a blood vessel because of its rapid growth. The patient may bleed out fatally.
* Cancers of hollow organs (intestine etc) can eat through the wall and lead to sepsis.
* This is infection of the tumour itself leading to sepsis
* The cancer deposits in organs can cause them to malfunction. Liver damage will lead to accumulation of toxins. Brain damage can lead to coma etc.
* Deposits around the lungs cause fluid to accumulate and patient slowly becomes unable to breathe

Ultimately death from any disease occurs via one of three modes – cardiac (heart unable to pump blood to feed your brain); respiratory (adequate oxygen cannot be provided) or brain (brain cannot signal the heart and lungs to function)

Cancers can expand so rapidly by being huge consumers of food, resources, and space that would otherwise be used by other normal cells. As normal organs face pressure (literal) and competition in food/air, they begin to fail.

It will kill you slowly if you don’t get it treated as soon as possible. Some cancer cells spread, some are not. Some are malignant, some are not. It depends on what cancer it is.