Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

Today we will talk about Lymphoma and Leukemia.

Let's start with hematopoietic cells which originated from two main cells Lymphoblast and Myeloblast. Lymphoblast cells develop eventually to lymphocytes (B & T cells). Myeloblast develop to three main cell lines which are the granulocyte, erythroid, and the megakaryocyte. If we get any tumor in the lymphoblast cell line (tumor arises from any cell), this causes the lymphoma; however, the myeloblast tumor causes leukemia (myeloid leukemia). The previously mentioned information was regarding the origin. For the site, we have two main concepts, the lymph nodes where the tumor of lymphocytes arises and causes lymphoma, and the blood and the bone marrow; if the neoplastic cells (the tumor lymphocytes) reach the blood or the bone marrow, it will be named leukemia (leukemia is a disease (cancer) arises in the bone marrow or the blood; however, Lymphoma is a disease arises in the lymph nodes).

Notes: -Lymphoma can arise in both the lymph nodes and the bone marrow.

-Leukemia arises in the blood and the bone marrow.

Hematopoietic neoplasm is different from all other cancer types. It's called fluid tumors. It doesn't form a mass, and it doesn't kill by physical damage like other cancers. (in leukemia) There is just circulating blasts (cancer cells) and they kill by different mechanism. Most important thing to know about that they damage the bone marrow itself (the place from where they originated), they (the myeloblasts) kill the normal cells there and cause anemia, leucopenia, and thrombocytopenia. Patients die because of bleeding or infection because of leucopenia. On the other hand, lymphoma forms a mass (the lymph nodes enlarge) but it doesn't kill. Both (leukemia and lymphoma) can go to the solid organs. However the main cause of the diseases is different and localized for each one, Lymphoma occurs in the lymph nodes as we said earlier, and leukemia occurs in the bone marrow, and then in the advanced levels they can go to the so solid organs. Leukemia kills more by thrombocytopenia which causes bleeding, or infection as a result of leucopenia.

Lymphoma is cancer of lymphocytes, it can begin at any stage of maturation. Historically they are classified into two types: Hodgkin lymphoma and non Hodgkin lymphoma.

Speaking about non Hodgkin lymphoma, It's further divided into two types: B and T lymphoma (because they either arise from B or T cells). Lymphomas mostly arise from lymph nodes but sometimes it goes out and then it's named as extranodal lymphoma (this means that sometimes it can arise from any organ and cause a damage in that organ).

How can we know if they are B or T cells?

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Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

Normally inside the lymph nodes there are germinal centers called follicles which represent the B cells, and what surrounds the germinal center is the paracortex which represents the T cells.

In lymphoma we get different morphology; a small lymphocyte proliferates and removes everything surrounds it to take its place. So under the microscope the shape and the color of the lymph node change. We still didn't answer the question above. So how we can tell if this cell is a B or T cell. We have a technique called immunophenotyping; this is a technique that helps us differentiate between B and T cells by special markers. B cells express certain markers and T cells express different markers.

Cluster of differentiation (CD markers) are used to identify each cell by its subtypes. For B cell the most common one is CD20. So what we usually do when we get a case of enlarged lymph nodes (lymphoma) is getting a stain of CD20, if the results are positive then it's a B cell type. T cells express CD3 (In general T cells can also express CD2, CD4, CD5, CD6, CD7, and CD8. They are called the early markers. However the most common one is CD3. Same thing with B cells they also express more than one type such as CD19, CD21, CD22… but the most common one is CD20). Hodgkin lymphoma is a special type of lymphoma. It doesn't express any of the B or T cell types markers, it expresses CD30 (we'll talk about it later).

Now we'll talk about famous types of lymphoma. There are too many types. According to the recent classification, nowadays we have around 200 types of lymphoma, so it needs a specialist to diagnose it.

1. Lymphoblastic lymphoma or Lymphoblastic Leukemia:

Lymphoblastic lymphoma and lymphoblastic leukemia are the same disease (the same cell of origin) but can arise in the bone marrow so we call it leukemia, and also it can arise in the lymph nodes then it's called lymphoma. This disease arises from the earliest cell which is the lymphoblast. Normally lymphoblast convert to lymphocyte; however, in the case of leukemia, mutation happens inside the lymphoblast which causes an arrest mutation which prohibits the cell from further maturating to lymphocyte, so it remains immature. The next level of mutation is proliferation of the immature cells. So we get a large amount of immature cells either in the lymph node or the bone marrow.

As we know that we have a T lymphoblastic leukemia and a B lymphoblastic leukemia. The B type is the more common one in general, and the most common one in children. It's an aggressive disease (always the diseases related with immature cells are aggressive).

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Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

2. Follicular Lymphoma:

Normally in the lymph nodes we have follicles which have a certain shape and arranged in a certain way. The cause of follicular lymphoma is mutations that happen in the cells of the germinal center which lead to proliferation of these cells. Unlike the lymphoblastic lymphoma, the follicular cells are mature ones. These cells arise from the follicular centers as B cells and then they begin to proliferate and as a result we get an enlarged lymph nodes full of follicles.

The picture below resembles the reactive follicular hyperplasia which we talked about last lecture. The same shape, it has many follicles, large, crowded and closed to each other which took the space of the paracortical area; however, the difference is that in this picture there is no reaction or inciting factors, and there is mutation while in the reactive one there is no mutation.

• But how can we tell which is which?!! It's important to know that there is mutation in follicular lymphoma, in which translocation between two chromosomes happens (the first one is 14 and the second is 18), on the 18 chromosome there is a gene Bcl2 (B cell lymphoma 2: its normal function is promoting the cell survival), it's considered as anti-apoptotic factor (in normal cells we have pro-apoptotic factors and anti-apoptotic factors which are balanced). At the beginning of the cell life the anti-apoptotic cells are the ones who work first to let the cell function well and keep it alive, after a while the pro-apoptotic factors start to function to allow apoptosis to take place when the cell is no

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Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

longer beneficial and functional. So Bcl2 is one of the anti-apoptotic factors which found on the 18 chromosome. On the 14 chromosome we have a gene IgH (immunoglobulin heavy chain: this is one of the active genes that result in making the immunoglobulin). In this follicular lymphoma a mutation occurs; Lymphoma cells have specific translocation (14:18), in which Bcl2 gene on chromosome 18 fuses with IgH gene on chromosome 14, causing overexpression of Bcl2 which in turn allows the cell to be functional for a longer time, and this results in accumulation of follicular cells (B cells) in a huge amount in the germinal center leading to the neoplasmic cancer. Still we have the question how we can differentiate the follicular lymphoma from the reactive follicular hyperplasia. Under the microscope both are alike, so we stain them with a stain against Bcl2, if the result is positive (ضاويه ) it indicates follicular lymphoma, and if the result is negative it indicates reactive follicular hyperplasia.

• Follicular lymphoma is most common among the elderly people, and it usually appears as a generalized one (all lymph nodes in the body are enlarged). The course of lymphoma is divided into high grade and low grades (for example, lymphoblast is one of the high grade. Follicular lymphoma is one of the low grade because it's mature cells, so it's slowly progressing). So, the course of the disease is called indolent (indolent means chronic, not aggressive one) which tells that it takes time until getting for progression (maybe 5, 10 or even 15 years the patient has cells which are easy stable but after this long time transformation occurs because of accumulation of many mutations inside which results in an aggressive form). Low grade lymphomas are usually not treated because its proliferation is low, and if we give them a chemotherapy it won't make this big change because they are proliferating in a stable manner, and they very close to the normal level. Treatment is given only when the disease is advanced.

3. Diffuse Large B Cell Lymphoma:

From the name you could tell that it's related to high grade lymphoma (by the word diffuse). In this type of lymphoma, the follicular centers and the paracortex disappear, and instead large immature cells take place. It arises either de novo (means without previous cause (primary)) or it arises secondery to other low grade lymphomas such as the follicular which after a while can give more mutations and transform to high grades. This type of lymphoma is the most common in adults. The morphology: Cells are large in size (double or more of the normal lymphocyte), and it invades the whole lymph node making neither follicle nor paracortex.

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Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

It is a high grade lymphoma, when they are treated by chemotherapy they usually respond to this chemotherapy and achieve remission. 80% of patients if treated with chemotherapy they respond but there still a chance of reoccurring later.

In the picture below if you look at the nuclei, they are large, and we can find between them small normal lymphocytes. These lymphoma cells you see them they are large (double or triple or more) and the chromatin is different in color which normally appears very dark.

4. Chronic Lymphocytic leukemia/Small Lymphocytic Lymphoma:

Chronic means that the cells are mature (the last phase), and they are the same as normal lymphocytes but they are in huge amounts; however, "acute" indicates the early phase which is the immature cell phase. It can arise in the lymph node (lymphoma) or in the bone marrow (leukemia). So it's named according to the place it arises in. These cells get mutation in the Bcl2 which will be overexpressed (different mechanism; there is no translocation) and this causes increase in the number of the cells since there is no apoptosis which eventually results in lymphoma or leukemia. This kind of leukemia (chronic) is the most common one in the elderly

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Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

people. The acute type is common in children (as we mentioned earlier in this sheet). Normally the number of the white blood cells (WBC's) is 10,000; however, in these patients the number of WBC's reaches 40,000 or 50,000. The same happens in the lymph nodes, large amount of small lymphocytes which enlarges the size of the lymph node. This disease is regarded as a low grade lymphoma, so we don't give chemotherapy for this kind of diseases.

Under the microscope, we see in the picture below large amounts of lymphocytes, they appear small and mature (like normal lymphocytes). Normal lymphocytes are fragile cells ( هشه so ,( خالياwhen there are large number of lymphocytes they collide and then burst and die. The burst cells are called "smudge cells" ( الممزقه which we see down in the picture (the black arrows) ,( الخالياamong the normal lymphocytes.

*All the previously mentioned lymphomas are non-Hodgkin. (B is the more common one and T is less common)

Hodgkin Lymphoma:

This is a special type of lymphoma was described 150 years ago by a surgeon called Hodgkin.

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Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

This disease has a special behavior and characteristic. Unlike follicular lymphoma, it arise in a localized limited area then contiguous spread occurs, commonly it starts from the neck then moves to the auxiliary lymph nodes and goes to the mediastinum, then to the abdomen and bone marrow and solid organs. This is the way it moves in the body (special characteristic) by a contiguous spread until the patient dies (there was no chemotherapy back then). Hodgkin could describe the disease clinically but after years the microscope was invented and they could use it to see these lymphoma under the microscope (they didn't know before using the microscope that this disease was a type of cancer). As we said Lymphoma in general are lymphocytes invading the whole lymph nodes leaving no place for follicular centers and paracortex; however, Hodgkin type is different, where the neoplastic cells are minority and you can see them surrounded by normal lymphocytes and other types of cells, so tumor here is formed but not directly by the neoplastic cells but by the reactive normal components. The malignant cells (neoplastic) have a special shape which was described by Reed and Sternberg as a distorted giant lymphocyte.

The picture below shows the giant distorted cell (the black arrow), it has two nuclei and inside them two large nucleoli (the nucleolus itself is bigger than the normal lymphocyte). This Reed-Sternberg is negative for both B and T cells markers, so they didn't know the origin of this cell until later they could know that it's a B cell of origin; however, it expresses CD30.

So to sum up, Reed-Sternberg cells are of B cell of origin. They are wide and they don't cause the disease by themselves, and they express the CD30. Its behavior is different from other cancers regarding the manner of spreading (contiguous spread).

*Hodgkin lymphoma in general forms 1/3 of lymphoma in adults, and the other 2/3 are non-Hodgkin. In children it's the opposite Hodgkin is more common and occurs in higher percentages.

Leukemia

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Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

As we know there are two origins of the hematopoietic cells ; we have the lymphoblast and the myeloblst . When we study blood cancer we have to classify blood tumors according to that ; so we have lymphoma related to the first lineage "lymphoblast" that is going to differentiate into B and T lymphocyte , and we have leukemia related to the second lineage "myeloblast" that is going to differentiate into megakaryocyte, erythrocyte and granulocyte " basophile , neutrophil , eosinophile and monocyte " .

Acute Myeloid Leukemia

This type of leukemia "AML" is a cancer starts from cells known as "myeloblasts" which is the earliest stage in the differentiation of the granulocyte . The cancer happen because of oncogenic arrest mutation that prevent the normal maturation of this cell and remain at the stage of myeloblast in addition to the high rate of persistent proliferation so we end with huge number of immature granulocytes "myeloblasts" . In normal the number of myeloblast cells doesn't exceed 10% of all the cells in the bone marrow ,but this is not the case in leukemia because these cells start to proliferate on the expense of the other cell types causing bone marrow failure . We call any abnormal proliferation of myeloblast as leukemia when the number of these cells become 20% or more of all the bone marrow cells , what in between is another disease called "pre-leukemia" we well talk about later . To diagnose this disease we observe the changes in the white blood cell count ; normally the only type of WBC circulating in the blood is neutrophil and any other previous stage of undifferentiated cells is absent from the blood because these cells exist only in bone marrow . However, in leukemia we start observing decrease in the number of WBC in the blood because of myeloblast abnormal proliferation in the bone marrow that exceeds the normal on the expense of mature WBCs , with time these abnormal cells destruct all the mature WBCs so there level in the blood decrease to zero , these abnormal myeloblasts then start to circulate in the blood which is "leukemia" ; so we start with normal WBC count then it decreases then it increases but all of these cells are myeloblasts .

AML differs from ALL "Acute Lymphocytic Leukemia " in that it can affect all ages from children to elderly people and it is even more aggressive than ALL .

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Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

This picture shows "Leukemia" because we can see blood cells which mean the myeloblast start to circulate in the blood and a comparison between the lymphoblast "left" and myeloblast "right" :

- Myeloblast is a large cell compared with the surrounding RBCs , and is slightly larger than the lymphoblast .

- Myeloblast has more abundant cytoplasm compared with the lymphoblast , and contain granules in its cytoplasm while the lymphoblast doesn't .

- Both cells have large nucleus but myeloblast nucleus contains a nucleolus "white dot " while the lymphoblast has no nucleolus .

Myelodysplastic syndrome

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Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

Myelodysplastic Syndrome MDS is a pre-leukemic disease, from the name "myelo" refers to bone marrow, "dysplastic" refers to dysplasia which is a stage before cancer. This disease starts with a mutation in myeloblast; this mutation inhibits the maturation of the myeloblast but not the proliferation, so their maturation is slow but no mutation affects the proliferation to make it rapid as in leukemia, the number of myeloblasts remain normal or above the normal but not more than 20% of all the cells in the bone marrow, so if the mutation affects the maturation and the number of the cells is between 5% to 20% this is MDS "pre-leukemia". This defect in maturation affects the three lines of cells "erythrocytes, neutrophiles and megakaryocytes" and results in: decreased number of normal neutrophils "immature", anemia because of the affected erythrocytes so the number of RBCs is reduced and thrombocytopenia because of abnormal maturation of megakaryocytes that give rise to platelets , so the hallmarks of MDS : in the blood "cytopenia: reduction in the blood cells" so we end with anemia, thrombocytopenia and reduction in neutrophils , while in the bone marrow we have slight increase in myeloblast number but not leukemia . MDS takes place only in adults and older age people compared with AML that can happen at any age, after a period of time this disease progress to leukemia if the number of myeloblast exceeds 20% .

Chronic Myeloid Leukemia

Chronic Myeloid Leukemia or CML contrasts CLL in lymphoid lineage, the same idea as CLL it is a chronic disease in which we have mature cells but here these cells are neutrophils instead of lymphocytes, these are mature cells but there proliferation is abnormal and they exceed the normal cell count 10,000 cells and may reach 100,000 or even more and all of these cells are neutrophils . In this disease the maturation is normal but there is a mutation in the proliferation, this type of leukemia is the first mutation to be discovered in cancer in seventies , it is a translocation involving the chromosomes 9 and 22; on chromosome 9 there is a gene ABL is translocated to the gene BCR on chromosome 22 and they fuse forming a totally different new gene BCR-ABL that function to produce a protein "Tyrosine Kinase" that promotes cell survival . These mutated cells continue to replicate producing new cells that contains the BCR-ABL gene and this gene elongate the half life of these cells from the normal "4 days" up to 100 to 200 days. Actually not only the neutrophil is affected by this disease but also eosinphils, basophils and monocytes "not lymphocytes" but the most frequent cell type to be observed in this disease is neutrophil .

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Mohammed Ghara & Ala'a MatarPathology sheet #2326/12/2013

Under the microscope we can diagnose MDS if we have large number of neutrophils surrounded by their precursors "myloblasts" in the blood and normally these present only in the bone marrow.

The treatment of this disease is by what is called targeted therapy in which they give antibodies against BCR-ABL mutated gene, and this is a new generation of chemotherapy other than the standard chemotherapy in which the antibodies are given to attack a mutated gene .

Good Luck

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