Why Does Cancer Treatment Often Make Your Hair Fall Out?

Dear SSS Readers,

During the week, a friend and I were chatting about an elderly lady who has recently been diagnosed with breast cancer. Luckily, the diagnosis was made very early and the outlook for treatment is promising. Unfortunately, she has found out that she will most likely lose her hair as a result of the chemotherapy. I am sure you have all heard of this scenario before. My friend, knowing that I am working with cancer cells in my job, asked me why this was. 

So why do people often lose their hair when they are on chemotherapy?

These days, cancer is unfortunately a part of our lives, and despite major advances in diagnostics and therapy, this disease is still a major cause of death all over the world.

Since this is not the first time someone (myself included) has wondered about hair loss and chemotherapy, I thought it would be an interesting topic to share with all our SSS readers :)

To write this post, I've touched on several topics, from cells to genes and DNA to cancer, and if anyone wants to know more or discuss any of these topics further, I would welcome comments and suggestions for future posts :)

Enjoy the post!!

Karen

What are Cells? 

As many of you may know, our bodies are composed of billions of building blocks called cells. 

These cells are the functioning units of our body ensuring that we can live and breathe, fight infection, see, hear, digest our food, reproduce and do all the other things that humans (and plants, animals and bugs do!). 

Different types of cells make up different organs (e.g. liver, heart, kidney, lungs), which in turn contribute to different systems (e.g. circulatory, reproduction, immune system), meaning that correct cellular function is absolutely essential for survival.

You will never observe cells just by looking at your skin because the cells are so tiny, and not visible to the naked eye. Each cell in the picture is about 40,000 times smaller than it looks! Within each cell are specialised compartments (called organelles) which drive the various functions of the cell. 

Diagram 2 below is a typical cartoon drawing of the inside of a human cell where you can see all the organelles and in particular the nucleus containing the DNA. Each cell has a single nucleus, and each nucleus contains exactly the same DNA.

Diagram 2

How then can we get so many different cell types, if they all appear to be the same and contain the same DNA? 

We have eye cells, skin cells, hair cells, liver cells, blood cells, kidney cells and the list goes on! 

The simple answer to this is that although each cell has the same genes, different cell types use different genes. In this way, you could think of the genes as switches, with certain switches off and other switches on at any given time. 

This system of having genes switched on and off in different cell types allows, for example, the cells in our eyes to control our vision so that we can see, while cells in our liver work hard to remove the toxins that build up when we drink alcohol.

However impressive our cells are, they do not live forever, and as they get old, they lose the ability to function as well as they used to, and they will eventually die and be replaced with new cells. This process is perfectly normal, and in fact, a great example of this is in our skin cells (Diagram 1), which are continuously being replaced with new healthy cells.

The controlled death of old cells and the generation and growth of new cells is all down to the action of genes. 

A cell needs nutrients in order to grow and divide and this we provide in the lab. The requirements for a cell to grow and divide in the body are very similar. A major requirement for cell division is the building blocks to make new DNA so that new cells (known as daughter cells) contain an exact copy of the DNA so that they too can function correctly and control their own cell division later on (shown in Diagram 3).

Diagram 3

This division of cells needs to be tightly controlled in order to both prevent cell overgrowth (which can result in warts, skintags and cancer) and also to make sure that we have enough cells to deal with injury (in the case of a healing wound where cells grow very fast). There are many genes present in the cells which are switched on and off in a controlled manner to coordinate cell division. 
If these genes fail to work correctly, or are switched on or off at the wrong times, cell division will become uncontrolled and cancer can result.

Cancer 

From what you've read above, you can probably imagine that a tumour is simply an overgrowth of cells. This overgrowth can occur for many reasons, and scientists are still trying to work out all the causes. Some people are born with genetic mutations that may make them more likely to develop cancer in their lifetime.  One example of this is breast cancer, which is said to run in families (however, not always). Other cancer types are caused  by sporadic damage to the genes from exposure to UV (damaging rays in the sunlight), cancer-causing agents in cigarettes and other agents known to cause mutations. The process of cell aging can also contribute to mutations, and this explains why we see so much cancer today - people are living longer than they did many years ago. 

Since cancer cells usually have an altered cell division program, and tend to rapidly divide to make up a tumour or to spread, they will have an even greater need for material to make new DNA and new cellular organelles than healthy cells. 

This characteristic of cancer cells is quite often exploited in chemotherapy approaches, whereby drugs are used to treat cancer.

Some cancer drugs are made to look like (or mimic) building blocks of DNA molecules. We will call this type of drugs nucleotide mimics, since nucleotides are the building blocks of DNA. Nucleotides are used to make new DNA molecules when a cell is doubling it's DNA during DNA replication before cell division as seen in Diagram 4. The DNA molecule looks like an open scissors during DNA replication, when nucleotides are added in to make the chain longer (see left hand side of Diagram 4).

Since cancer cells divide rapidly, they have an increased demand for cellular building blocks, including nucleotides, since the DNA must double or replicate before each cell division. When nucleotide mimics are given to patients with cancer, they will be taken into the rapidly dividing cancer cells and will cause serious problems during DNA replication. Unfortunately, these drugs can also be used during DNA replication in rapidly growing healthy cells, such as the cells that produce hair, leading to hair loss.

For a closer look at what's going on with nucleotide mimics, Diagram 4 shows two scenarios. On the left, we see normal nucleotides (which are shown as the letters A, G, C or T). These are taken up into the DNA molecule during cell division. What's important to note here is that each nucleotide has a yellow cap at the end, and this allows addition of the following nucleotide and therefore building of a 'chain'. On the right, we see a scenario where nucleotide mimics are present (marked by arrows). Notice that these look very similar to the normal nucleotides, but have an orange cap instead of a yellow. The cell now has a mixture of nucleotides to use, those with yellow caps and those with orange caps. The mimics are similar enough to be taking up into the DNA molecule, but  the orange cap prevents them from making a chain of nucleotides and so the 'chain' gets broken, and correct cell division cannot occur. This causes cells to die. 


Diagram 4. DNA replication

Healthy cells, who have a 'normally' controlled pattern of cell division can recognise that there is a problem  when the nucleotide mimics are present, and they can slow down to fix this problem. However, cancer cells are dividing so fast and uncontrolled that they cannot 'put the brakes on' to fix the damage, and therefore will most likely die after a few rounds of cell division. 

This trick with using nucleotide mimics sounds very clever, and it is in fact one of the most clever chemotherapeutic strategies to date (in my own opinion). Several other similar strategies exist, whereby the drugs consist of molecules that mimic cellular nutrients. However, all with all drugs, these have side effects. One such side effect is that these types of drugs can also have effects on some of the body's healthy cells, in particular those that divide very rapidly. This is where the hair loss comes in. The cells that grow hair are found in the hair follicle (Diagram 5). The matrix stem cells inside the follicle are rapidly dividing giving rise to new hair cells all the time, and so they too have a high demand for materials, nutrients etc. Because of this, they end up 'tricked' into using the chemotherapy drugs, and this causes the hair to fall out. 



Diagram 5

But the good news is, that unlike cancer cells, the cells of the hair matrix are healthy, and will usually quickly recover, so if someone loses their hair due to chemotherapy, it will almost always grow back when the treatment is over :)

I hope you have all enjoyed this post, and please just write if you have more questions.

Happy Easter to all!

References

Cancer Research UK website
http://education.technyou.edu.au/

Wikipedia
http://www.baileybio.com

www.macmillan.org.uk
Hair follicle: Morgan, 2006. Upending the Hair Follicle. Nature Genetics 38:273-274. DOI: 10.1038/ng0306-273