All of the following are characteristic features of Burkitt lymphoma EXCEPT:

Explanation

## Burkitt Lymphoma: Key Features ### Characteristic Cytogenetics & Molecular Features **Key Point:** Burkitt lymphoma is defined by translocation t(8;14)(q24;q32) in ~80% of cases, placing the MYC oncogene under control of the immunoglobulin heavy chain (IgH) enhancer on chromosome 14. Variant translocations t(2;8) and t(8;22) occur in ~20% of cases but involve MYC with kappa or lambda light chain loci. ### Histopathology **High-Yield:** The **starry sky pattern** is pathognomonic — a background of uniform medium-sized lymphoid cells (the "sky") interspersed with tingible body macrophages containing apoptotic debris (the "stars"). This reflects the extremely high mitotic rate and apoptosis. ### Immunophenotype **Clinical Pearl:** Burkitt lymphoma is **CD5-negative and CD23-negative**. This is a critical distinguishing feature: - **CD5+ and CD23+** = Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) - **CD5+ and CD23−** = Mantle cell lymphoma - **CD5− and CD23−** = Burkitt lymphoma (and follicular lymphoma) Burkitt cells are CD19+, CD20+, and surface immunoglobulin+, but the absence of CD5 and CD23 is diagnostic. ### Proliferation Rate **Key Point:** Ki-67 proliferation index is extremely high (>95%), reflecting the aggressive nature and short cell cycle time. This is one of the fastest-growing human malignancies. ### Summary Table | Feature | Burkitt | CLL/SLL | Mantle Cell | | --- | --- | --- | --- | | **t(8;14)** | Yes (80%) | No | No | | **CD5** | Negative | Positive | Positive | | **CD23** | Negative | Positive | Negative | | **Ki-67** | >95% | Low (10–30%) | Intermediate–high | | **Histology** | Starry sky | Diffuse small cells | Mantle zone pattern | **Warning:** Do not confuse Burkitt lymphoma with mantle cell lymphoma. Both are CD5-negative in Burkitt but CD5-positive in mantle cell — this is the key discriminator. ## Why Option 3 (CD5 and CD23 Co-Expression) Is Wrong Burkitt lymphoma is **CD5-negative and CD23-negative**. Co-expression of both CD5 and CD23 is characteristic of CLL/SLL, not Burkitt lymphoma. This is the correct answer because it does NOT apply to Burkitt lymphoma.