4. Leukemia and Lymphoma

What cells do blood cancers actually come from?

All of the types of blood cancer fit into two categories: myeloid and lymphoid.  Lymphoid cells include natural killer cells, B-cells and T-cells; myeloid cells include red blood cells, platelets and all the white blood cells except B-cells and T-cells.  This classification is based on evidence that all myeloid cells come from one type of stem cell, and all lymphoid cells from another.  Almost every blood cancer specifies somewhere in its name whether it’s myeloid or lymphoid. Some cancers mention in their name the more specific cell type they originate from – for instance erythroblastic leukemia originates from erythroblasts, which are immature red blood cells. Note that multiple myeloma has a bit of a counterintuitive name – its lymphoid not myeloid.

Why does it matter if my cancer is lymphoid or myeloid?

Whether a cancer is lymphoid or myeloid is significant for cancer care because different chemotherapies tend to have different effectiveness on myeloid vs lymphoid cancers. This is in part because different mutations contribute to the transformation of myeloid vs lymphoid cells into cancer.  Lymphoid vs myeloid cells also interact differently with other cell types, which can result in different complications – for instance, the cancerous cells of acute myeloid leukemia can trigger blood clotting, while those of acute lymphoid leukemia typically cannot.

What’s the difference between leukemia and lymphoma?

Leukemias arise in the bone marrow, while lymphomas almost always arise outside of the bone marrow. Unlike leukemias, lymphomas arise from lymphatic tissue, which occurs throughout the body. All lymphomas develop from lymphoid cells, while leukemias can arise from either myeloid or lymphoid cells. Because leukemias develop inside bones and from cells that don’t stick together well, leukemias don’t produce a ‘lump’. In contrast, lymphomas arise in softer tissues and do form lumps. However, just cutting out the lump can’t cure lymphoma. This is because the cells lymphoma develops from don’t stick together that well – they move apart and start growing in other parts of the body before lymphoma can even be noticed. Lymphoma cells can even spread into the bone marrow, and in rare cases can arise in lymphatic tissue within the bone marrow. Almost always though, lymphoma starts out as a lump somewhere outside the marrow. Leukemias can also spread to lymphatic tissue, but because they are leukemias they by definition start in the bone marrow. There are cases where by the time the disease is noticed, cancer cells are in both lymphatic tissue and the bone marrow, and we can’t tell where they were first – in those cases it’s arbitrary whether they’re called leukemia or lymphoma.

What are the differences between the signs of leukemia and lymphoma?

Since lymphomas originate physically away from the area where blood cells are produced, the bone marrow, lymphomas tend to initially have only small effects on blood cell numbers. In contrast, leukemias can change blood cell numbers quite a lot. It’s the altered blood cell numbers that produce many of the initial symptoms of leukemia (i.e. anemia, bleeding, bruising, susceptibility to infection). In contrast, lymphoma symptoms are more related to the lymphoma cells using the body’s energy, resulting in weight loss and weakness, and triggering immune response, resulting in fever and night sweats.

What’s the difference between the types of lymphoma?

There are two main types of lymphoma – Hodgkin and Non-Hodgkin. Hodgkin lymphoma was originally noticed as something different because the cells looked different. In a Hodgkin lymphoma mass, there are many different cell types, including distinctive looking lymphoid cells called Reed-Sternberg cells. In Non-Hodgkin lymphoma, cancerous masses are filled almost entirely with identical looking cancerous lymphoid cells. Distinguishing Hodgkin and Non-Hodgkin is important for choosing a treatment. Lymphomas can be further classified by exactly where it arises and exactly what cell type is affected (usually B or T-cells but sometimes natural killer cells).

What’s the difference between acute and chronic leukemia?

To distinguish between acute and chronic leukemia, we need to ask another question: are the cells maturing? Cell maturation is, in a way, like human maturation – growing up and becoming able to do a certain job.  Leukemias in which the cancer cells can mature completely are called ‘chronic’ and those in which the cells can’t are called ‘acute’. It is true that ‘chronic’ leukemias do tend to progress more slowly, but the terms acute and chronic actually refer to whether cancer cells can mature.

What causes the symptoms of acute leukemia?

The majority of acute leukemia cancer cells remain trapped in the bone marrow. They take up so much space that the marrow doesn’t have room to make the usual amounts of the normal blood cells. The number of normal blood cells drops, resulting in anemia, bruising and bleeding and sometimes infections– all of these are the initial symptoms of acute leukemia.  Thus it’s the lower numbers of normal cells, not the cancer cells themselves, that give the initial symptoms of acute leukemia.

How did my blood test suggest I have acute leukemia?

Low levels of normal blood cells may be noticed on blood tests in acute leukemia. Also, some of the immature cancer cells (‘blasts’) escape into circulating blood and may be noticed on blood tests.

How did my blood test suggest I have chronic leukemia?

In chronic leukemia, cancer cells are still produced in the bone marrow, but can mature and can easily enter the blood. The increased number of mature cells in the blood may be noticed on blood tests as a sign of chronic leukemia.

What causes the symptoms of chronic leukemia?

Since cancer cells in chronic leukemia do leave the bone marrow, they take up less space in the marrow, and interfere less with the marrows production of normal cells. Symptoms are instead related to use of lots of the body’s energy and resources to make all the cancer cells. This leads to fatigue and weight loss. The spleen can also be affected – it may become enlarged as cancer cells accumulate there. An enlarged spleen can cause symptoms if it presses against other organs.

 

References

Leukemia and Lymphoma Society of Canada. Disease and Support Information. July 11 2013. Available at http://www.llscanada.org/?gclid=COr5jbK34roCFQVgMgodfl4AMQ#/diseaseinformation/. Accessed Nov 2013.

Chapter 12. Hematopathology. In: Kemp WL, Burns DK, Brown TG. eds.Pathology: The Big PictureNew York: McGraw-Hill; 2008.http://accessmedicine.mhmedical.com.ezproxy.library.ubc.ca/content.aspx?bookid=499&Sectionid=41568295. Accessed February 09, 2014.

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