Hem-oncology (blood cancers), Part 1: Blood.

My first focus is going to be around blood cancers. Hematology is the branch of medicine concerned with blood so the study of blood cancers is called hem-oncology. First of all, to understand the many different types of blood cancers, we have to understand what blood is, what it’s made of, and how it works.

So what is blood? Why do we have it? Why is it red? Do we have our blood for life?

Image: Blood cell development diagram, from hematopoietic stem cell to mature blood cells.

Blood is simply a ‘carrier’ around your body. Much like a river that enables the transport of goods from one city to another, your blood transports oxygen, nutrients (broken down food essentially), and your immune system around your body. Of course it’s a lot more complex than that but it is basically a life saving transport mechanism.

The majority of blood is composed of red blood cells, which are a unique type of cell, as they do not contain a nucleus or DNA!! Without DNA red blood cells lack the ability to replicate and divide, like most cells can, and consequently, red blood cells have a life span of only a few months. So your blood is constantly renewing itself, and every few months, every single red blood cell that you have inside you now will be gone.

Red blood cells’ function is to transport oxygen around the body so that all the other cells can use it to metabolise glucose (sugar from your food) and grow, or do what ever that cell is designed to do. To do this, red blood cells contain a protein called haemoglobin, which oxygen essentially binds to after it is absorbed by your lungs, and is then released around your body.

There are two other main types of cells found in your blood: white blood cells (leukocytes), and platelets (thrombocytes). Collectively, blood cells are known as hematocytes, or haematopoietic cells, if you’re feeling fancy! White blood cells are essentially your immune system, and their functions involve developing antibodies against bacteria and viruses, or in the case of macrophages, they physically eat up foreign material in the body. Surprisingly, some white blood cells live for only a few days before dying and being replaced with new cells, however, some of your most important white blood cells, the memory T-cells, can last for years. White blood cells are extremely important, as it is from these cells that multiple blood cancers emerge, such as leukaemias, lymphomas, or another blood cancer known as multiple myeloma, to name but just a few.

Platelets are the other type of common blood cell, they are sometimes known as yellow blood cells, but much less commonly than red, or white blood cells are. As with red blood cells, platelets do not contain a nucleus, and hence, no DNA, so they too cannot replicate, and have a life span of around 5-10 days. The most important job of platelets are to form blood clots when you are cut. So when you cut yourself, and you see your blood slowly become crusty, and harden, that is your platelets in action! A common side effect of many cancer treatments, especially in hemtology, is a decrease in the number of platelets, known as thrombocytopenia. This is a particularly dangerous situation, as even the smallest cut might be unable to clot, and so you become at risk of bleeding out. Grim.

As well as the three major types of blood cells discussed above, your blood contains a variety of many different cells, see the diagram above for the range of blood cells floating about you right now! Notice the presence of erythrocytes (red blood cells), neutrophils, eosinophils, basophils, lymphocytes, and monocytes (all types of white blood cells), and thrombocytes (platelets)? The majority of blood, however, consists of a liquid called plasma, which acts as a medium for the blood cells to travel through the body. And is also an important substance for the transport of nutrients (food!) round your body. Ever cut yourself and all you see is a clear liquid? That is blood plasma.

Basically, blood is complicated, and so is the cancers that can evolve from it. My main focus for my first blog series will be around the leukaemias (notice I made leukaemia plural? You might have just heard leukaemia mentioned as one disease before but this is far from the truth). Right now I want you to have a look at the diagram above again. Blood cells renew very frequently, and they all develop from blood stem cells (you might have heard of stem cells before!), called haemocytoblasts or ‘multipotential haematopoietic stem cells’. These cells are essentially the godfathers of blood cells, and can evolve into every single blood cell in the right situation. The first stage of development splits the ‘blood-god’ cell into two different types: myeloid progenitors, and lymphoid progenitors.

These two cell types are extremely important in the formation of some of the blood cells discussed above, but when things go wrong, these white blood cells can cause two chronic blood cancers named Chronic Myeloid Leukaemia (CML) when affecting the neutrophils, eosinophils, and basophils (known collectively as granulocytes), or Chronic Lymphocytic Leukaemia (CLL) when affecting the B-cell lymphocytes. There are two other types of the most common leukaemias: Acute Myeloid Leukaemia (AML) and Acute Lymphocytic Leukaemia (ALL). You can see the major difference between these cancers are the words acute/chronic and myeloid/lymphocytic and this depends on which stage the cancer develops in the diagram shown above: acute leukaemias form early on from the progenitor cells (also known as blast cells), while the chronic leukaemias form from the more mature cells, nearer the bottom of the diagram.

I hope you can begin to appreciate just how complicated cancer actually is. It is not just one disease. Even ‘leukaemia’ is not just one disease, it is at least four, and this is just the beginning. In Part 2 of Hem-oncology I will go into further depth on the complexity of blood and we’ll begin to see how the lymphocytic leukaemias (ALL and CLL) develop.

Thank you for reading, and I appreciate your feedback or suggestions.