Currently Burkitt's lymphoma can be divided into three main clinical variants: the endemic, the sporadic, and the immunodeficiency-associated variants.
The endemic variant (also called "African variant") most commonly occurs in children living in malaria endemic regions of the world (e.g., equatorial Africa, Brazil, and Papua New Guinea). Epstein-Barr Virus (EBV) infection is found in nearly all patients. It is believed that chronic malaria reduces resistance to EBV, allowing it to take hold. The disease characteristically involves the jaw or other facial bone, distal ileum, cecum, ovaries, kidney or the breast.
The sporadic type of Burkitt lymphoma (also known as "non-African") is the most common variant found in places where malaria is not holoendemic. The tumor cells have a similar appearance to the cancer cells of classical endemic Burkitt lymphoma. Sporadic lymphomas are rarely associated with the Epstein–Barr virus. Non-Hodgkin lymphoma, which includes Burkitt's, accounts for 30–50% of childhood lymphoma. The jaw is less commonly involved, compared to the endemic variant. The ileocecal region is the common site of involvement.
Immunodeficiency-associated Burkitt lymphoma is usually associated with HIV infection or occurs in the setting of post-transplant patients who are taking immunosuppressive drugs. Burkitt lymphoma can be one of the diseases associated with the initial manifestation of AIDS.
By morphology (i.e. microscopic appearance) or immunophenotype, it is almost impossible to differentiate these three clinical variants. Immunodeficiency-associated Burkitt lymphoma may demonstrate more plasmacytic appearance or more pleomorphism, but these features are not specific.
Normal B cells of a germinal center possess rearranged immunoglobulin heavy and light chain genes, and each isolated B cell possesses a unique IgH gene rearrangement. Since Burkitt lymphoma and other B-cell lymphomas are a clonal proliferative process, all tumor cells from one patient are supposed to possess identical IgH genes. When the DNA of tumor cells is analyzed using electrophoresis, a clonal band can be demonstrated, since identical IgH genes will move to the same position. On the contrary, when a normal or reactive lymph node is analyzed using the same technique, a smear rather than a distinct band will be seen. This technique is useful since sometimes benign reactive processes (e.g. infectious mononucleosis) and malignant lymphoma can be difficult to distinguish.
The tumor consists of sheets of a monotonous (i.e. similar in size and morphology) population of medium size lymphoid cells with high proliferative activity and apoptotic activity. The "starry sky" appearance seen under low power is due to scattered tingible body-laden macrophages (macrophages containing dead body of apoptotic tumor cells). The old descriptive term of "small non-cleaved cell" is misleading. The tumor cells are mostly medium in size (i.e. tumor nuclei size similar to that of histiocytes or endothelial cells). "Small non-cleaved cells" are compared to "large non-cleaved cells" of normal germinal center lymphocytes. Tumor cells possess small amount of basophilic cytoplasm with three to four small nucleoli. The cellular outline usually appears squared off.
The tumor cells in Burkitt lymphoma generally strongly express markers of B cell differentiation (CD20, CD22, CD19) as well as CD10, and BCL6. The tumour cells are generally negative for BCL2 and TdT. The high mitotic activity of Burkitt lymphoma is confirmed by nearly 100% of the cells staining positive for Ki67.
All types of Burkitt's lymphoma are characterized by disregulation of the c-myc gene by one of three chromosomal translocations. This gene is found at 8q24.
The most common variant is t(8;14)(q24;q32), which accounts for approximately 85% of cases. This involves c-myc and IGH@. A variant of this, a three-way translocation, t(8;14;18), has also been identified.
A rare variant is at t(2;8)(p12;q24). This involves IGK@ and c-myc.
Another rare variant is t(8;22)(q24;q11). This involves IGL@ and c-myc.
Combined, the two less-common translocations, t(2;8)(p12;q24) and t(8;22)(q24;q11), account for the remaining 15% of cases not due to the t(8;14)(q24;q32) translocation.
Unique genetic alterations promote cell survival in Burkitt lymphoma, distinct from other types of lymphoma. These TCF3 and ID3 gene mutations in Burkitt correspond to a cell survival pathway that may be found to be amenable to targeted therapy.
Treatment may be dose-adjusted EPOCH with Rituxan (rituximab) or the modified Magrath regimen (R-CODOX-M/IVAC).
The effects of the chemotherapy, as with all cancers, depend on the time of diagnosis. With faster growing cancers, such as Burkitt's, the cancer actually responds faster than with slower growing cancers. This rapid response to chemotherapy can be hazardous to the patient, as a phenomenon called "tumor lysis syndrome" could occur. Close monitoring of the patient and adequate hydration is essential during the process.
Treatment with dose-adjusted EPOCH with Rituxan (rituximab) has shown an 8 year survival rate of 91% for low risk, 90% for low-intermediate risk, 67% for high-intermediate risk, and 31% for high risk cases with few of the side effects associated with Burkitt's lymphoma chemotherapy.
^Turgeon, Mary Louise (2005). Clinical hematology: theory and procedures. Hagerstown, MD: Lippincott Williams & Wilkins. p. 283. ISBN0-7817-5007-5. Frequency of lymphoid neoplasms. (Source: Modified from WHO Blue Book on Tumour of Hematopoietic and Lymphoid Tissues. 2001, p. 2001.)