Karyotype in Burkitt's Lymphoma
The most likely karyotype finding in Burkitt's lymphoma is t(8;14)(q24;q32), which represents the MYC-IGH translocation. 1
Cytogenetic Characteristics of Burkitt Lymphoma
Burkitt lymphoma (BL) has a characteristic cytogenetic profile involving the MYC gene on chromosome 8. The translocation t(8;14) is the hallmark genetic abnormality found in approximately 80% of Burkitt lymphoma cases 2. This translocation juxtaposes the MYC oncogene from chromosome 8q24 with the immunoglobulin heavy chain (IGH) locus on chromosome 14q32, resulting in MYC overexpression.
Primary and Variant Translocations in Burkitt Lymphoma
- Primary translocation (80%): t(8;14)(q24;q32) [MYC-IGH]
- Variant translocations (20%):
- t(8;22)(q24;q11) [MYC-IGL]
- t(2;8)(p12;q24) [IGK-MYC]
All these translocations result in the same functional outcome - deregulation and overexpression of the MYC oncogene, which drives the aggressive proliferation characteristic of Burkitt lymphoma 1, 2.
Distinguishing Features from Other Lymphoma Karyotypes
To understand why t(8;14) is the correct answer, it's important to differentiate it from the other karyotypes mentioned:
- t(9;22) - This is the Philadelphia chromosome, characteristic of chronic myeloid leukemia and some acute lymphoblastic leukemias, not Burkitt lymphoma
- t(14;18) - This translocation involves BCL2-IGH and is the hallmark of follicular lymphoma (found in approximately 85% of cases) 3
- t(15;17) - This is pathognomonic for acute promyelocytic leukemia, not Burkitt lymphoma
Diagnostic Significance
The identification of MYC rearrangements through cytogenetic analysis is essential for the diagnosis of Burkitt lymphoma. According to European recommendations for cytogenomic analysis, Burkitt lymphoma is characterized by "t(8;14); MYC-IGH, and IGK/IGL variants, with no additional involvement of BCL2 or BCL6 or complex karyotype" 1.
The NCCN guidelines further emphasize that BLs generally exhibit a simple karyotype, with MYC translocation involving an immunoglobulin gene as their sole abnormality 1. This contrasts with diffuse large B-cell lymphoma (DLBCL), which typically has a more complex karyotype that may include various combinations of MYC, BCL2, and BCL6 rearrangements.
Clinical Implications
The presence of the t(8;14) translocation has important clinical implications:
- Confirms the diagnosis of Burkitt lymphoma when integrated with morphological and immunophenotypic findings
- Distinguishes true Burkitt lymphoma from Burkitt-like lymphoma with 11q aberration, which lacks MYC rearrangement 1
- Helps differentiate BL from double-hit or triple-hit lymphomas that have MYC rearrangements along with BCL2 and/or BCL6 translocations
Molecular Mechanisms
The t(8;14) translocation in Burkitt lymphoma can occur through different molecular mechanisms:
- In endemic BL (African type), the translocation often occurs during V-D-J recombination of immunoglobulin genes 4
- In sporadic BL, the translocation frequently arises during immunoglobulin isotype-switching 4
In both cases, the end result is the same - constitutive activation of the MYC oncogene leading to uncontrolled cell proliferation.
In conclusion, while other chromosomal abnormalities may be present in some cases of Burkitt lymphoma, the t(8;14) translocation is the defining cytogenetic feature of this aggressive B-cell malignancy.