Clinical Pathology: General Principles, Hematology & Coagulation, Immunology & Histocompatibility, Urinalysis, Body Fluids, Clinical Microscopy, Genetic Testing

448) A 16-year-old boy is taken to the emergency department with abdominal pain that has worsened over the past week. He complains of abdominal tenderness and reveals that he has not had a bowel movement for the past 4 days. The patient is sent for a computed tomography (CT) scan of the abdomen, which shows a large abdominal mass and dilated loops of bowel suggestive of obstruction. He is scheduled for exploratory laparotomy, and his preoperative peripheral smear is shown in the figure. Which one of the following is true regarding the patient’s diagnosis?

• Burkitt lymphoma/leukemia is a mature B-cell malignancy of germinal center origin (CD10 positive). The leukemic form is equivalent to the French-American-British (FAB) L3 B-acute lymphoblastic leukemia (ALL) characterized by expression of CD20 and surface immunoglobulin (sIg) and absence of terminal deoxynucleotidyl transferase (TdT).

• There are three clinicopathologic types of Burkitt lymphoma (BL):

     Endemic BL is a childhood disease mainly affecting those in equatorial Africa and is almost always Epstein-Barr virus (EBV) positive.

     Sporadic BL is seen throughout the world, affecting children and young adults (median age, 30 years) and is EBV driven in approximately 30% of cases.

     Immunodeficiency-associated BL, often in association with human immunodeficiency virus (HIV), is not uncommonly the initial manifestation of the disease.

• Cytologically, the cells are characteristically medium sized with a deep-blue rim of cytoplasm and lipid-filled cytoplasmic vacuoles. Many mitotic figures are usually identified.

• In tissue, there is a characteristic starry-sky appearance due to the monotonous cell population and scattered tingible body macrophages. Ki-67 staining is typically positive in more than 95% of the cells.

• The cytogenetic hallmark of this malignancy is rearrangement of the c-Myc locus on chromosome 8 with a number of fusion partners (IgH-chromosome 14, Igλ-chromosome 2, Igκ-chromosome 22).

• Because the neoplastic cells have such a high turnover rate, aggressive chemotherapy can cure most patients with BL. Tumor lysis can occur after chemotherapy induction (hyperkalemia, hyperphosphatemia, hyperuricemia and hyperuricosuria, hypocalcemia, and consequent acute uric acid nephropathy and acute renal failure).

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