5. Lymphoma 1 - Multidisciplinary Flashcards
What is the definition of lymphoma?
neoplasm of the lymphoid cells
Where is lymphoma usually found?
- Lymph nodes, bone marrow and/or blood (lymphatic system)
- Lymphoid organs: spleen or gut-associated lymphoid tissue
- Skin (often T cell disease)
- Rarely ‘anywhere’ (CNS, ocular, testes, breast)
What percentage are Non-Hodgkin vs Hodgkin lymphoma?
80% = Non-Hodgkin and 20% = Hodgkin
How many types of lymphomas are there and why?
There are > 60 different types of lymphoma because they all originate from different points in the maturation of lymphocytes. B cells go through several stages when they are developing. You get different types of lymphoma/leukaemia based on the point at which the tumour arises.
How does immunoglobulin and T cell receptor gene recombination allow antibodies to recognise a huge number of different antigens?
- We have a set of germ line genes that we can recombine to make a diverse variety of different antibodies and T cell receptors
- This recombination (know as VDJ recombination) will occur in the bone marrow
- Within the germinal centre, there is a second stage of DNA alteration which involves class switching and the insertion of nucleotide point mutations at the sites of VDJ recombination (known as somatic hypermutation) to generate even more diversity
- These phenomena make it possible for antibodies to recognise a huge number of different antigens
What is the downside of an adaptive immune system?
- The process of VDJ recombination and somatic hypermutation runs the risk of causing recombination errors and new point mutations
- Lymphocytes are reliant on apoptosis to keep their massive proliferation under control (90% of lymphocytes will die in the germinal centre)
- This ensures antigen specificity and prevents autoimmune disease
- If mutations turn off apoptosis, it can lead to malignancy
- Rapid cell proliferation in the germinal centre increases the risk of DNA replication error
Why are Ig promotors in B cells highly active?
Because they are designed to be able to produce loads of immunoglobulins
If, by some error, you translocate an oncogene downstream of the promoter, then you get malignant genes being expressed, such as:
Bcl2, Bcl6, Myc, cyclinD1
What are known risk factors for lymphoma, and what is the risk factor identified in the majority?
Majority have NO identifiable risk factor.
Know risk factors: Constant antigenic stimulation, infection (direct viral infection of lymphocytes), loss of T cell function
Can lymphomas be caused by constant antigenic stimulation?**
Yes - This is initially antigen-dependent, but then becomes autonomous?
What can H pylori infection lead to?
Gastric MALT marginal zone NHL of the stomach
What can Sjogren syndrome lead to?
Marginal zone NHL of parotid lymphoma
What can Coeliac disease lead to?
Small bowel T cell lymphoma, EATL (enteropathy-associated T cell non-Hodgkin lymphoma)
What viruses can cause lymphoma?
E.g. HTLV1, EBV
What virus is associated with lymphoma by direct viral integration?
HTLV1
How does HTLV1 cause lymphoma?
Infects T cells by vertical transmission
Who tends to carry HTLV1?
Caribbean and Japanese carriers
What virus may lead to developing adult T cell leukaemia lymphoma? And why?
HTLV1. This is very aggressive. This is caused by a virus integrating into the T cell genome, driving proliferation and transforming the cells
Why virus causes lymphoma by immunosuppresion?
EBV
How does EBV cause lymphoma?
EBV infects B lymphocytes and when the EBV is quiescent, it is doing nothing to the B cells. The healthy carrier state is maintained by cytotoxic T cells killing EBV antigen expressing B cells. Loss of T cell function leads to risk of EBV-driven lymphomas. T cell function can be lost due to HIV or iatrogenic (organ transplant immunosuppression) - later leads to post-transplant lymphoproliferative disorder (PTLD)
What types of lymphoreticular tissues are there as part of the lymphoreticular system?
Generative LR tissue, reactive LR tissue, acquired LR tissue
Where is generative LR tissue found?
Bone marrow and thymus
Where is reactive LR tissue found?
Lymph nodes and spleen
Where is acquired LR tissue found?
Extra-nodal lymphoid tissue (e.g. skin, stomach, lung).
What is the function of generative LR tissue?
Generation/maturation of lymphoid cells
What is the function of reactive LR tissue?
Development of immune reaction
What is the function of acquired LR tissue?
Development of local immune reaction
What are the cells of the lymphoreticular system?
B and T lymphocytes, and accessory cells
What is the purpose of B lymphocytes (in the context of the lymphoreticular system)?
Express surface Ig, responsible for antibody production
What is the purpose of T lymphocytes (in the context of the lymphoreticular system)?
Express surface T cell receptor, regulation of B cells and macrophage function, cytotoxic function
What types of cells are accessory cells?
Antigen-presenting cells, macrophages, connective tissue cells
What is normal lymph node histology?
- The rounded areas are the B cell follicles
- In between the B cell follicles you have the T cell areas
- The medulla is the central area where mature B cells eventually end up
(See notes)
What is the mantle zone?
In a lymphoid follicle, the crescent shaped region is the mantle zone where naive unstimulated B cells are located
What is the germinal centre?
B cells will then migrate into the paler round area (germinal centre) where they encounter antigen-presenting cells and undergo activation and selection.
What is a predisposing factor for lymphoma in the germinal centre?
There is a lot of cell turnover in this area
What does the T cell area of a lymph node contain?
Consists of lots of T cells, antigen-presenting cells and high endothelial vessels
What happens in the T cell area of the lymph node?
This is where T cells that bind antigen epitopes are selected and activated
How can we detect and identify lymphocytes?
Lymphocytes can be identified based on their type and stage of maturation by looking at the different types of cell surface receptors expressed by the cells.
There are > 100 CD markers. They can be detected using immunohistochemistry.
What are the main markers to identify B and T lymphocytes?
CD20 for B cells and CD3 and CD5 for T cells
What is the (histological) definition of lymphoma?
Neoplastic proliferation of lymphoid cells forming discrete tissue masses
What site are lymphomas found in?
Arise in and involve lymphoid tissues (including acquired lymphoid tissue - extranodal lymphoma)
What is the basic WHO classification of lymphoma?
Hodgkin Lymphoma: classical and lymphocyte predominant.
Non-Hodgkin Lymphoma: B cell (more common) - precursor B cell neoplasms, peripheral B cell neoplasms (Low grade, High grade); T cell (rarer) - precursor T cell neoplasms, peripheral T cell neoplasms.
How is lymphoma classified?
Lymphoma is classified using a combination of clinical, histological, immunohistochemical and molecular data resulting in well-defined entities with distinct behaviour. This has implications on treatment and prognosis.
Why does immunosuppression lead to lymphoma?
Immunosuppression increases the risk of lymphoma because it predisposes to infection and also leads to a loss of surveillance of cell replication
What is the most common type of lymphoma? And what % of cases?
B Cell Non-Hodgkin Lymphoma is the MOST COMMON type (80-85%)
What stage of lymphocyte development and activation do lymphomas form?
Can arise from different stages of lymphocyte development and activation. (So, in some lymphomas the neoplastic lymphoma cells will look pretty similar to the normal counterpart in terms of morphology and the pattern of CD markers)
Where do you tend to find neoplastic lymphoid cells? and what is the exception?
Neoplastic lymphoid cells circulate in the blood (this is why it is often disseminated at presentation). NOTE: Hodgkin’s lymphoma is an exception because it tends to only affect one or two lymph node groups.
How may patients develop immunodeficiencies as a result of lymphomas?
Lymphoid neoplasms can disrupt the normal immune system
What type of B cell lymphomas are there from the bone marrow?
Precursor B lymphoblastic lymphoma(/leukaemia), small lymphocytic lymphoma, chronic lymphocytic leukaemia
What types of T cell lymphoma is there from the thymus?
Precursor T lymphoblastic lymphoma (/leukaemia)
What type of B cell lymphoma is there from the mantle zone of lymph nodes?
Mantle cell lymphoma
What types of B cell lymphomas are there from the germinal centre?
Follicular lymphoma, Burkitt lymphoma, diffuse large B cell lymphoma, Hodgkin lymphoma
What types of B cell lymphomas are there from the post germinal centre?
Diffuse large B cell lymphoma, marginal zone lymphoma, small lymphocytic lymphoma, chronic lymphocytic leukaemia
What types of T cell lymphomas are there from the post germinal centre?
Peripheral T cell lymphoma
What type of B cell lymphoma is there from after the lymph node?*
Multiple myeloma