A 17-year-old boy is brought to the emergency department for progressive fatigue. The patient developed a cough 2 weeks ago, and for the past few days, he has become more tired due to difficulty breathing, particularly when lying down at night. Temperature is 38.2 C (100.8 F), pulse is 120/min, and respirations are 34/min. Examination shows distended neck veins. The lungs have diminished breath sounds, particularly on the left side. Bruising and diffuse petechiae are present on the trunk, and the mucous membranes appear pale. Chest radiography reveals a large mediastinal mass with a left pleural effusion. The effusion is drained, and examination of the fluid shows many immature hematopoietic cells, consistent with blast forms. Immunophenotyping of these cells would most likely reveal which of the following predominant markers?

Question

A 17-year-old boy is brought to the emergency department for progressive fatigue.  The patient developed a cough 2 weeks ago, and for the past few days, he has become more tired due to difficulty breathing, particularly when lying down at night.  Temperature is 38.2 C (100.8 F), pulse is 120/min, and respirations are 34/min.  Examination shows distended neck veins.  The lungs have diminished breath sounds, particularly on the left side.  Bruising and diffuse petechiae are present on the trunk, and the mucous membranes appear pale.  Chest radiography reveals a large mediastinal mass with a left pleural effusion.  The effusion is drained, and examination of the fluid shows many immature hematopoietic cells, consistent with blast forms.  Immunophenotyping of these cells would most likely reveal which of the following predominant markers?

Quizplus · Accepted Answer

11ec160b_3969_0d3c_9249_65a4e39b7ab0_MD0001_00 This patient's mediastinal mass, concurrent signs of bone marrow failure (eg, petechiae, pallor), and blasts in the pleural fluid are findings worrisome for acute lymphoblastic leukemia (ALL). Expansion of the mediastinal mass frequently compresses adjacent structures such as the superior vena cava (venous swelling of the head/neck), esophagus (dysphagia), and trachea (dyspnea). Pleural effusions, caused by inflammation from tumor growth and cytokine release, also commonly occur. The neoplastic cells of ALL arise from lymphoid precursors of either B or T lineage. In a patient with a mediastinal mass and suspected ALL, T lymphoblasts are usually the cells of origin due to their location within the thymus during lymphocyte maturation. In contrast to B-lymphoblastic leukemia (B-ALL), which typically presents in early childhood, T-lymphoblastic leukemia (T-ALL) classically affects adolescents/young adults. Flow cytometry of bone marrow aspirate, peripheral blood, or pleural effusion can be used to characterize the cell of origin. Terminal deoxynucleotidyl transferase (TdT), a DNA polymerase involved in V(D)J recombination (generates antigen receptor diversity during early B- and T-cell maturation), is expressed only by lymphoid progenitor cells. The following markers are used to classify cell lineage: Therefore, this patient with a presentation consistent with T-ALL likely has blast cells positive for TdT and CD3. (Choice B) CD15 and CD30 are consistent with classic Hodgkin lymphoma, which can present with a mediastinal mass and superior vena cava syndrome in adolescents. However, Reed-Sternberg cells, not blast cells, would be expected. (Choice C) CD20 (a B-cell marker) and surface immunoglobulin (a marker unique to B cells) are seen in B-cell malignancies. B-ALL usually occurs in early childhood and is less likely to be associated with a mediastinal mass compared to T-ALL. (Choice D) CD33 and myeloperoxidase are markers characteristic of myeloid lineage. A mediastinal mass is far more commonly associated with ALL than acute myeloid leukemia. Educational objective: T-lymphoblastic leukemia often presents in adolescents with a mediastinal mass that can cause respiratory symptoms or superior vena cava syndrome. The diagnosis is confirmed via flow cytometry by identifying a population of T lymphoblasts (ie, TdT and CD3 positive).

A 17-Year-Old Boy Is Brought to the Emergency Department for Progressive