Hello everyone and welcome to this week's blog post where I will discuss blood cancer, the fifth most common type of cancer in the UK. In this blog post, I will discuss what cancer is, the symptoms and diagnostic methods of blood cancer and the scientific debate behind whether blood cancers can metastasise
Cancer is the uncontrollable division of cells by mitosis, which leads to the growth of abnormal cells. Cancer can occur anywhere in the body, including in the brain, bones and the blood. The etymology of the word 'cancer' stems from around 400 B.C. when the great physician Hippocrates (read my blog post on him here) described a tumour as resembling a crab - because of its leg-like projections of blood vessels stemming from the main body. As such, this disease was referred to as 'karkinos', or 'crab' in Greek.
Blood cancers can typically be split into two different groups. The first is acute blood cancers, which are aggressive, fast-growing cancers which spread quickly around the body. The second group are chronic blood cancers, which are slower-growing so take longer to spread around the body. All types of blood cancer which I describe below can also be described as acute or chronic. Of these, acute blood cancers are generally more dangerous as sufferers become ill very quickly and rarely know they have blood cancer until after they have been admitted to hospital.
Generally, according to the NHS, the symptoms of blood cancers develop over time and become more severe as the number of abnormal cells increases. These symptoms include tiredness, bone and joint pain, swollen lymph nodes, weight loss and easily bruised skin. For a more complete list of symptoms, click here.
For the most part, people who are suspected of suffering from a type of blood cancer required to visit a hospital or GP surgery to have a blood test. The blood is then analysed to confirm a diagnosis. This is done by using a machine to count the number of different types of blood cells you have. The blood is also sometimes smeared onto a microscope slide and analysed to check for any visible abnormalities in their shape. Additionally, bone marrow biopsies can also be performed, where a bone marrow sample is taken before being analysed under a microscope as before to check for any cancerous cells. Furthermore, scans such as X-rays may also be taken to determine whether any of your organs have been damaged.
Before describing the different types of blood cancer, it is important to understand how blood cells are made in the human body. All blood cells are produced in the bone marrow, which is a soft, spongy tissue which is found in the centre of many bones in the body. At birth, all bone marrow is red bone marrow. As you age, however, this red bone marrow gets converted into the yellow bone marrow. Red bone marrow, which is found in flat bones and on the ends of long longs such as femurs, is responsible for the production of red blood cells, platelets and most white blood cells. Meanwhile, yellow bone marrow, which is found in the centre of long bones, is responsible for the production for more white blood cells.
Bone marrow can produce blood cells as they contain a type of stem cell called hematopoietic stem cells. As you know stem cells are incredibly important in the growth of an organism as they can differentiate into other types of cell, while at the same time not reduce in number. These hematopoietic stem cells differentiate into other stem cells, such as lymphoid and myeloid stem cells, which then can further differentiate into lymphocytes, red blood cells and other types of blood cell. These cells then either move to other parts of the body, such as the thymus gland in the case of T lymphocyte cells, where they mature before being released into the cardiovascular system.
Blood cancers can occur when this initial stage of production does not occur correctly, as there are mutations in some or all of these hematopoietic stem cells. As a result of this, the blood cells which are produced are abnormal. Not only does this mean that they can't carry out their function, but they are also sometimes unable to destroy themselves (by apoptosis) when their lifespan is complete, causing a build-up of faulty blood cells in the bloodstream.
According to the National Foundation for Cancer Research in the United States, leukaemias are the most common form of cancer in children. Leukaemia occurs when mutations occur causing white blood cells to become cancerous. Consequently, these abnormal cells occupy much-needed space in the body, eventually outnumbering the healthy cells and hindering their immune response, resulting in a suppressed immune system and making suffers more prone to being infected from common and usually harmless infections. Additionally, white blood cells can also mutate causing lymphoma (which is caused by mutations in lymphocytes) and myeloma (which is caused by the mutation of plasma cells).
There is some debate in the scientific community about how often blood cancer metastasises. Metastasis is when cancerous cells, which are dividing uncontrollably by mitosis, migrate from the original site of cancer and implant themselves into other tissues, where they continue to divide. As such, a cancerous tumour then forms in this new location due to these metastatic cancer cells. Some argue that the metastasis of blood cancers is rare as the stem cells which divide are trapped inside the bone so can't easily spread around the body. Indeed, according to OncologyNurseAdvisor, while cancers of the blood can metastasis, it is very rare for it to form tumours in other organs. Meanwhile, a paper published in 2015 argued that leukaemia has inherent properties which make it more likely to metastasise.
The science behind the theory outlined in the paper is solid. Normally, when cancer metastasis, it first must invade nearby healthy tissue, and then continue moving through this surrounding tissue until it reaches the bloodstream. These stages are called local invasion and intravasation respectively. In the metastasis of leukaemia, however, leukocytes are already present in the bloodstream, so don't need to go through those steps. Additionally, for cancer to metastasise, it must be able to infiltrate into a new area of the body and begin growing there. This stage is called extravasation. Leukocytes have an innate advantage in this stage, as they already have the ability to do this due to their function in the immune system.
Sources:
Mukherjee, S., 2011.The Emperor Of All Maladies. London: Fourth Estate.
Trendowski, M., 2015. The inherent metastasis of leukaemia and its exploitation by sonodynamic therapy.Critical Reviews in Oncology/Hematology, 94(2), pp.149-163.
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