Our cells need a few very important things to survive. They need oxygen, which is essential for energy production in cells. Without it, they’re mostly unable to produce energy and will eventually die. Cells need food. The food we eat breaks down and provides cells with the food they need. When we eat and digest, food is broken down into the building blocks that our cells use to grow and create new cells. But how do oxygen and food get to the cell? Through the blood.

Our lungs take in oxygen from the air and transfer it to the blood found in microscopic vessels. That blood then circulates back to the heart and is pumped throughout the body. Food takes a similar but slightly different route. After food leaves our stomachs and enters our intestines, nutrients are slowly absorbed into cells that line our gut. Those nutrients are then transferred into the blood. This blood then circulates to the liver, where it’s filtered to remove toxins and harmful molecules that may have gotten in. Then, just like the oxygen-rich blood from the lungs, nutrient-rich blood goes to the heart and is circulated throughout the whole body, delivering nutrients to your cells. Together, all of the organs and vessels that hold, filter, and move blood make up the circulatory system.

See, tumours are different. They don’t have the luxury of being supplied by blood vessels like healthy tissue does. The question is: is that a good or a bad thing? The answer is more complicated than you might think. Fundamentally, a tumour growing that is directly attached to a blood supply is bad. Those vessels can supply blood with nutrients and oxygen, allowing for faster growth and more aggressive cancer. On top of that, cancer can use blood vessels as a highway to quickly traverse the body. But tumours usually grow within a tissue, and they won’t have a dedicated blood supply. That means that they won’t have easy access to nutrients and oxygen. Immediately, you might think “good, no food and oxygen means they can’t grow”, which is a good instinct, but that might not be strictly true.

As a tumour grows, it depletes oxygen in its surroundings. If it doesn’t have a blood vessel, there’s no active supply, and they create an oxygen-deprived environment. This does, of course, make it harder for them to grow, but it also has other effects.

The process of a cancer cell causing blood vessel formation is called “angiogenesis”, meaning the genesis of vessels.

Tumours growing their own blood supply is a major issue. It, of course, creates the obvious issue of supplying oxygen and nutrients to the tumour. This lets a previously stunted tumour grow and divide rapidly. It also supplies the energy required for migration, helping a localized tumour spread.

Apart from that, it also provides more opportunities for cancer to spread into the blood. Because of the abnormal nature of cancer, it doesn’t do things quite properly. The ability to create new blood vessels is crucial for us as healthy organisms, not just in disease. It happens as we grow from embryos, supplying blood vessels to each tissue. But blood vessel formation doesn’t just occur in embryos; it’s also important in adults for wound healing and ovulation. But in cancer, it doesn’t happen quite right. In particular, blood vessels caused by tumours are often leaky.

Healthy blood vessels are composed of tightly woven layers of cells, so tightly woven that they can even hold liquid. That makes it harder for cancer to slip between the gaps and get into the bloodstream. But in cancer, the new vessels are patchy, with cells missing and holes throughout. That means cancer can make its way right into the bloodstream with no barriers at all. This is a huge issue, helping cancer spread from a single tumour throughout the whole body.

The circulatory system is essential for our health, and being able to grow new vessels is still important, even in adulthood. However, in the case of cancer, it has severe consequences. It leads to more nutrients, more oxygen, and more opportunities for cancer cells. So what if we target that? Being able to prevent tumours from creating new blood vessels sounds like a great idea. It could prevent blood supply to the tumour, keeping the tumour starved of nutrients and oxygen. Additionally, we could prevent the formation of leaky vessels and avoid easy access to the bloodstream, slowing the spread of cancer cells from the tumour.

Unfortunately, just like before, it’s not so easy. Targeting blood vessel formation has several problems, one of which is leading back to the oxygen-deprived tumour state. Just as before, without oxygen, the tumour might grow more slowly temporarily, but it also leads to more vessel formation. In fact, some trials looking at blocking blood vessel formation actually saw worsened outcomes, with more aggression and invasion of those cancers. At this point, researchers are trying to come up with ways to target blood vessel formation in cancer while avoiding the side effects. Some scientists are trying to find ways to destabilize the new vessels that tumours form, making them so unstable they don’t form at all. It’s a fascinating idea, but we’ll have to wait and see how it plays out.

I hope you learned a little something today, but next week we’re getting specific and talking about some of the different types of melanoma.

See you next week!

If you missed last week’s letter, you can read “Straight To The Point” to learn a little more about nanogels and how they’re used to deliver drugs.