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  • Emily Poulin

When Good Cells go Bad: What is Cancer?

Updated: Aug 6, 2019



It comes in all shapes and sizes. Sometimes it is caught early, sometimes it is found too late. Sometimes it leaves survivors, sometimes it does not.

But we all have the same questions about cancer: What is it and how does it develop? Is it genetic? Is it environmental? Is there any way I can prevent it?

Scientists around the world are constantly working to provide answers to all of these questions...

But today we can start with the first one.

What is cancer and how does it develop?

According to Google, each of our bodies contains 37.2 trillion cells. Cells are the basic unit of life, the smallest living things, often called the "building blocks of life" (this might be one of the more standard quotes from any biology class). Cells make up tissues, which make up organs, which make up organ systems, with each cell playing a role in making sure our bodies function normally every day, a state scientists call homeostasis.

Just like us, each individual cell has a life cycle: they are born, they grow, some divide in two to give rise to new cells, and then they die. When these steps operate normally, we have successfully achieved homeostasis.

Now imagine that one or more of these steps gets screwed up.

No more homeostasis.

This is the basis of cancer – when normal cells of the body behave abnormally, particularly in a way that gives them an advantage.

Imagine the Hunger Games of cells: cells that develop an abnormal ability to grow faster and divide more often than their neighbors will make more of themselves, more cancer cells that in turn, make more cancer cells. Then imagine the even greater advantage if a cancer cell were able to escape its natural death and continue making more of itself. Eventually, these abnormal cells will outcompete their neighbors, who do not have such growth and survival advantages.

How does one normal cell get messed up so badly that it becomes a deadly tumor?

The key: DNA.


DNA is a master genetic blueprint, of which every cell in the body has a copy. Each person's collective DNA is called their genome.

On an overall level, each of our genomes are what makes us unique, carrying the plans that allow just two cells (the sperm and egg) to build an entire person. This is because our genomes contain all the information every cell needs to function. When something happens to the DNA of a cell, the normal operation of that cell may be affected, and it could start to act abnormally.

One of these "somethings" is called a mutation.

A mutation is essentially a spelling mistake in the DNA code. While it might seem like DNA must be quite complicated to contain the blueprint to build an entire human, it is written using only four letters. Each of our genomes is approximately three billion letters - or base pairs - long and is estimated to measure about six feet (!).

A mutation occurs when any one of the DNA base pairs (the four letters, A, C, G, and T) is substituted for another, is deleted, or gains additional base pairs.

Let's illustrate this by mutating the word "monkey".

Substitution mutation: molkey

Addition mutation: monkeys

Deletion mutation: onkey

You can see these mutations either change the meaning of the original word or make the word unintelligible.

The same is true for DNA mutations. Some mutations are silent, which means that although the code itself changes, the meaning of the code does not. Others (like the examples above) are not silent, and do change the meaning of the DNA code. These types of mutations are the ones that can change how a cell operates.

Some mutations might turn something off, while others might turn something on.

For example, if a mutation turns off the mechanism that causes a cell to die, it will survive.

Alternatively, a mutation could turn something on or prevent it from being turned off, like a signal to grow. If a signal for a cell to grow became stuck on at all times, the cell would continue to grow when it was not supposed to.

How does one abnormal cell turn into cancer?

Not every abnormally behaving cell turns into a tumor. And not every mutation results in an abnormally behaving cell. Among other things, it comes down to the advantages granted by each mutation.

Once a mutation occurs in a cell's DNA, that same mutation will be passed down to all of its daughter cells. If the advantages are great enough that the original mutated cell can divide and generate more cells with that mutation, the greater the chance those cells will begin to form a tumor.

How do mutations occur?

There are two types of mutations: those we are born with (these are responsible for the so-called hereditary cancers) and those we acquire over the course of our lifetimes (these are generally not passed down to our children unless they randomly occur in sperm or egg cells).

Every time a cell divides in two, it must copy its DNA. This enables the original cell to keep one copy, and to pass another copy to its daughter cell. To do this, molecular machinery in the cell copies all three billion bases of the genome.

Imagine you had to hand copy three billion letters every few days. How many typos would you make?

Luckily, our cells have a backup system and a spell check step always occurs. Although the built-in spell check is exceptionally good, it may miss an occasional mistake, the result of which is a mutation, which now becomes a part of that cell's DNA. Depending on where they occur, these spontaneous mutations could be harmless, or could disrupt a cell's activities.

Alternatively, mutations can come randomly from exposure to the world around us. There are certain environmental exposures we know cause DNA mutations that might lead to cancer, like sunlight and smoking.

We hear a lot about wearing sunscreen and avoiding tanning booths. This is because UV radiation directly causes mutations in the DNA of our skin cells.

Remember that not all mutations will lead to cancer, but probability tells us that increased exposure increases the chances. Greater exposure to UV radiation over the course of a lifetime therefore increases the chances that a mutation will occur. This is why it's important to wear sunscreen regularly. Even if you don't get a sunburn, your skin cells are still being exposed to UV rays.

I wrote recently about tobacco use and its connection to lung cancer. You guessed it! Tobacco (particularly cigarettes) contains carcinogens, which can be anything that causes cancer, and may include things that cause DNA mutations. Smoking directly exposes cells in the lung to these carcinogens. Again, the rules of probability apply: not every mutation will result in cancer, but the more cigarettes one smokes, the greater the chance a cancer-causing mutation might occur.

Finally, mutations can also be genetic, or present from birth. Unlike the mutations induced by sunlight or smoking, which only occur in certain types of adult cells, hereditary mutations are present in every cell of the body from birth. Perhaps the most famous of these is the BRCA1 mutation. Women who are born with a BRCA1 mutation are more likely to develop breast or ovarian cancer and can pass the mutation on to their children.

BRCA1 is a gene present in every one of our genomes that contains the code for part of the DNA spell checking machinery. When the BRCA1 gene contains a mutation, it results in faulty spell checking. A faulty spell check can fail to correct random mutations that occur when cells copy their DNA. Therefore, BRCA1 mutations predispose a cell to develop additional mutations, thereby increasing the risk of cancer.

So what can I do?

We are consistently bombarded by stories in the news about new things that cause cancer. There are SO many things now, how are we even supposed to go outside without getting cancer?

Be aware of the facts, but also be realistic. It's not realistic to hide from the sun, but we can be smart about wearing protection if we are in the sun for long periods of time. Remember that not every mutation will result in cancer.

We should also be aware that whether a substance is considered a carcinogen is context-dependent. You will read more about this here soon, but it is important to remember that:

"Carcinogens do not cause cancer at all times, under all circumstances. Some may only be carcinogenic if a person is exposed in a certain way (for example, swallowing it as opposed to touching it). Some may only cause cancer in people who have a certain genetic makeup. Some of these agents may lead to cancer after only a very small exposure, while others might require intense exposure over many years" (from the American Cancer Society's website).

Finally, it is important to get screened. If we have a known family history, have smoked in the past, or have had a number of severe sunburns, we can be proactive.

Interested in learning more about cancer? Get in touch by emailing me with your interests for future topics!


#mutation #genome #DNA #cancer #BRCA1 #UVradiation #smoking

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