Thread by @AlexPetrovnia

It's a question I hear often, rife with misunderstandings, and one that matters to a huge number of people every day. So let's talk about it.
Why can’t we cure cancer? 🧵

In short, because it’s not a single disease. Cancer describes a mechanism of disease, not a specific disease. This would be like asking “why can’t we cure viral infections?”
So a better question is “why are cancers so hard to cure?”

That answer has a lot to do with the way cancers work, and what makes them cancers. A cancer is categorized by cell growth that’s unregulated. This means that a tumor will appear, and create a blockade to normal bodily functions in tour body.

Depending on where this happens, it might be very serious or not. It also depends on the qualities of the cancer cells themselves. To explain this more, we’re going to have to understand how cells reproduce themselves, and how cancer cells use that same cellular machinery.

Cells reproduce themselves by splitting themselves into two, over and over and over. This means that one cell can produce two "daughter" cells, and those two "daughter" cells can produce two "daughter" cells of their own. This quickly makes a huge number of cells!

This is how humans can go from a single cell (when an egg and sperm join to create the first cell) to an organism of TRILLIONS. The average human body has about 37 trillion cells in it! And in order to repair your body, your body makes about 230 billion new ones every day!

But wait a minute, if we're constantly producing new cells, how are we not constantly getting larger? The answer lies in the system that our body uses to control our growth, regulate healing, and even to maintain bodily systems.

Cells will keep reproducing themselves until they're "told" to stop by chemical signals in our body. These chemical signals are absolutely crucial to normal functioning, and so have several "backup" systems to prevent failure.

One of these is called "apoptosis", and it kills the cell. Many apoptosis events are "scheduled" for the cell after it reproduces a certain number of times, and help to make sure that our body makes new cells only where they're needed.

But when there are so, so, so many cells, sometimes even the backups fail. In very rare occasions, a cell is born that has failures in every system to control cell growth. This is cancer.
These systems are coded in the DNA of each and every one of your cells.

When we say that something "can cause cancer", what we mean is that something is a "mutagen", or a factor that can make mutations in your DNA more likely. These mutations can add up to increase the risk that a cell will be born with broken safeguards against uncontrolled growth.

So why is it such a big deal when a cell keeps reproducing? It's just one cell, right? Well, let's look at the growth of a system that doubles itself with each iteration. After 10 cycles, one cell becomes 1024. After 50 cycles, it becomes 1,125,899,906,842,624 cells.

So when a cell becomes cancerous, it begins duplicating itself at a dangerous rate. This is why tumors occur, where a cell is reproducing in the same place until the cells at that location begun to press on the surrounding tissue, because they simply take up too much room.

This space issue is what makes cancer so dangerous, and so variable. Depending on what the mass of cancerous cells is in the way of, depending on what bodily systems are disrupted, it could be an irritation, or it could be fatal.

Cancers can also vary in severity based on how exactly their cellular machinery is broken. Some grow faster than others, and some can be slowed down by certain body systems or by medical intervention even if they cannot be fully stopped.

Okay, so now that we understand what a cancer is, we can understand why it's so hard to treat, and so difficult to "cure".
The short answer is this; cancer is extremely difficult to treat because the cancerous cells are also your cells.

What I mean by that is this; the majority of our medicine is based on cellular chemical warfare. We treat bacterial infections with "antibiotics", which are chemicals that specifically interrupt the functioning of bacteria cells, but not human cells.

The problem with treating cancer is that cancer cells *are* human cells. So how do you develop a chemical weapon that kills cancer cells, but doesn't kill healthy human cells?
It's very, very difficult.

This issue is also why so many of the chemical (chemotherapy) treatments that we have for cancers also cause people to get very sick. Even though the cancer cells are attacked and killed, healthy cells are as well, and this takes a toll on the person being treated.

Radiation treatments have a similar issue. They kill human cells. When targeted very specifically, they can kill cancer cells (and hopefully a minimal number of healthy cells in the process), and potentially relieve a person of cancer.

Surgical treatments simply try to cut out all the cancerous cells, and kill them outside the body. If the cells can be successfully all cut out, the individual will be cured. But this is also difficult because cells are so, so small that it can be very difficult to get them all.

Another issue with all of these strategies is the possibility of cancer coming out of remission. This happens because it is extremely difficult to be certain that one has removed every single one of the cancerous cells.

As we learned earlier, even a single cancer cell can quickly become dangerous because of how quickly it duplicates.
However, our bodies are incredible enough that most people will have cancerous cells arise that they never know about.

The vast majority of cancerous cells that arise are eliminated by protective systems in the body to keep us safe from this very issue.

So even though today's lesson was a bit grim, I believe it's also very important for people to understand. I hope this has helped put a lot of the conversation around cancers into perspective and scientific context.

Some takeaways:
Stop asking science to "cure" cancer.
Take steps to protect yourself from mutagens that may increase your risk of cancers.
Appreciate the miracles that are both the body's natural defenses against cancer and modern medicine.

*your
*screams*