What is blood cancer?

Where does it come from?

Blood cancer is caused when something goes wrong with the development of your blood cells. It can affect your blood, bone marrow or lymph nodes. It should be considered a disease of the immune system since in the vast majority of cases the cells that are affected are the white blood cells which fight off infections. Indeed lymphocytes the very cells that are meant to produce antibodies to fight off infection are the origin point of much leukaemia and lymphoma. No wonder then that at the beginning of the Coronavirus crisis the experts warned Blood Cancer patients were at high risk whatever stage of their illness they were in.

There are many different types of blood cancer most of which are rare but together blood cancer is the 5th most common type of cancer so you are not alone!

Blood cancer is given strange sounding names linked to the different types of blood cell affected (see illustration above). Some of the names are usually shortened to three letters as otherwise they can be quite hard to say. The components of the name often indicate where the cancer is growing, and how fast it is growing, and an indication of what the cancer cells look like.

Lymphoma is when blood cancer mainly grows in the lymph nodes. There are many types of lymphoma but they almost all come from B-Lymphocytes.

Luekaemia is the name given to blood cancer when it mainly grows in the blood. The word “leukaemia” comes from the Greek for “white blood”.

Multiple Myeloma is the name given to blood cancer that comes from plasma cells and grows in the bone marrow.

Myelodysplastic syndromes (MDS) or Myelodysplasia and Myeloproliferative neoplasms (MPN) are cancers that form from blood stem cells in the bone marrow.

Acute or Aggressive means a fast growing form of blood cancer that tends to grow quickly and often needs treatment straight away. Nowadays some acute blood cancers can sometimes be cured. Examples include Acute Myeloid leukemia (AML), Acute Lymphoblastic Leukemia (ALL) which both grow in the blood and bone marrow and progress very quickly if not treated, and some types of lymphoma including Hodgkins and Diffuse Large B-cell Lymphoma (DLBL). In the past acute blood cancers all had low survival rates but now some of these cancers can be cured in the majority of cases.

Chronic or Indolent means a slow growing form of blood cancer that may not need treatment straight away but can often be harder to cure. Often people are put onto “watch and wait” which can sometimes mean “watch and worry”. This phase of not needing to be treated can sometimes last many years. When treated the cancer often responds well, but may sometimes return months or years later. Chronic blood cancers may need repeated treatments, but patients will often survive for many years, even in some cases decades. Examples include some types of lymphoma, Chronic Myeloid Leukemia (CML), and Chronic Lymphocytic Leukemia (CLL).

Leukemia, lymphoma or both? The curious case of CLL and SLL

We could group CLL and lymphomas together and call them “Lymphocyte Blood Cancer” This is further grouped and named by what the cancerous lymphocytes look like under the microscope.

B Lymphocytes seem to give rise to blood cancer quite often and give rise to a huge variety of types of cancer. There are actually more than 30 sub types of Non Hodgkins Lymphoma alone. Doctors will remove (biospy) tissue from the blood, lymph nodes, or the bone marrow and carefully examine the lymphocytes under a microscope to identify which precise type of blood cancer the patient has since this affects how aggressive the cancer is and how it should be treated.

Pathologists label the cells with different stains or markers, and even run genetic tests to see which genes have become corrupted and either mutated or been deleted in the cancerous lymphocytes.

When people hear about the mutations and deletions used to classify lymphocyte blood cancers they often assume that these are present in all their cells. In fact these changes are what makes the lymphocytes become cancer.

When all the tests are complete the doctor can identify which type of lymphocyte blood cancer we are dealing with and how they think it will behave.

For example will it grow quickly and be an acute cancer or will it grow slowly and be a chronic cancer? This all then determines whether you need treatment and which treatment should be used.

This is all based on how the lymphocytes look, what stains make them look different, and what genetic changes they have. Very occasionally it can be difficult to identify the lymphocytes. In that case an expert laboratory will be asked to have another look. In some cases a different diagnosis will then be made. This can feel quite worrying but it helps to realise that all along you had a lymphocyte blood cancer.

How the cells look predicts how fast the blood cancer grows and how it behaves. So in what is called Hodgkins Lymphoma the lymphocytes now look like owls, and they multiply quickly. The name “Hodgkins” is just the name of a doctor who first described this type of blood cancer.

Lymphocyte blood cancers without such owl cells are called Non- Hodgkins Lymphoma.

There are lots of types of lymphocyte blood cancers that go under the heading of Non Hodgkins lymphoma. Most of them are also named by what the cells look like under the microscope.

In Follicular lymphoma you can see clumps of lymphocytes that form follicles which are supposed to look a bit like hair follicules! In Diffuse Large B-Cell Lymphoma (DLBL) the lymphocytes are more spread out (diffuse) and are much larger compared to CLL.

One strange example of a type of lymphocyte blood cancer is Chronic Lymphocytic Luekaemia (CLL). The cancerous lymphocytes look small under the microscope. Even though CLL grows in the blood it is also described as a type of Non Hodgkins lymphoma. This is because CLL can’t seem to decide whether it wants to behave like a leukaemia or a lymphoma. CLL is therefore considered to belong to both types of blood cancer. Sometimes the lymphocytes only grow in the lymph nodes when it is called Small Lymphocytic Lymphoma (SLL). Whether in the blood or the lymph nodes CLL cells are identical and behave in exactly the same way. You might sometimes see CLL/SLL used as a name to cover this disease. But if the cells are growing in the blood it should be called CLL, no matter where else they are also growing in that person.

Other types of Blood Cancer

Multiple Myeloma cells are from plasma cells and can identified under the microscope in bone marrow. Some are “binucleate” which means they have two nucleus. These cells tend to grow and cause bone pain, and release a specific antibody which tends to swamp the ordinary antibodies and so (like lymphocyte blood cancer) makes the immune system less effective.

Myelodysplastic syndromes (MDS) or Myelodysplasia lead to too few blood cells being formed in the bone marrow as instead immature cells are formed. Myeloproliferative neoplasms (MPN) also start int the bone marrow and tend to lead to too many of one of the types of blood cell being formed.

What does all this mean?

We know so much about blood cancer because often the cells are relatively easy to obtain and study. And as a result it has been subcategorised into so many different types. It can get a bit confusing. Increasingly other types of cancer are also being subdivided in a similar way but people tend to talk about “Breast Cancer” or “Bowel Cancer” rather than the name of a specific type. By thinking of “Blood Cancer” as a whole we are able to demonstrate how common it actually is. Many of the sub types of blood cancer are quite rare. But taken together blood cancer is the most common form of cancer in children, the 5th most common in adults, and sadly despite a rapid rate of advance in treatment it does remain the 3rd most common cancer killer. Blood cancer patients can learn from others with different sub types to them as there are definitely some overlaps in the type of experiences patients have, and the types of treatment used. Even with the same type of blood cancer the way it behaves in an individual patient can sometimes hugely vary. Do not assume you will have the same journey of any individual patient you read about. And if you are diagnosed with a blood cancer today there are now more treatments available than even just a few years ago. Over the years to come we can also expect a lot of progress as even more new treatments are being studied at the moment.