Pathology – MCQ 39 – 17 year-old boy with increased TLC and 80% blasts

A 17 year-old boy presented with TLC of 138 x 10 (9) /L with 80% blasts on the peripheral smear. Chest X-ray demonstrated a large mediastinal mass. Immunophenotyping of this patient’s blasts would most likely demonstrate:
a) No surface antigens (null phenotype)
b) An immature T cell phenotype (Tdt/D34/CD7 positive)
c) Myeloid markers, such as CD13, CD33 and CD15
d) B cell markers, such as CD19, CD20 and CD22

Correct answer : b) An immature T cell phenotype (Tdt/D34/CD7 positive)

There is increased lymphocytes with 80% blasts – indicating acute leukemia. Also the age group and the mediastinal mass point out to the possibility of T cell leukemia. (T cell leukemia is usually seen in adolescent boys with thymic involvement). Hence the blasts would demonstrate immature T cell phenotype