Immunophenotyping of T-cell acute lymphoblastic leukaemia: Practical hurdles

Background: The 2016 WHO classification of T cell acute lymphoblastic leukemia suggest that cases of pre and pro T-cell Acute Lymphoblastic Leukaemia (T-ALL) now fall under Early T-cell precursor ALL (ETP-ALL) or Near ETP-ALL. Accurate subtyping is essential as the subsets are characterized by distinct molecular profiles and identifying molecular aberrations allow patients to receive novel treatment agents. Aim and Objectives: To study the immuno-phenotypic characteristics in T-ALL cases and assess the diagnostic difficulties encountered in its subtyping. Material and Methods: Thirty-seven cases of T-ALL were analysed on flow cytometry using a 6/8 colour panel of monoclonal antibodies, including B cell, T-cell, myeloid and stem cell markers. The cases were categorized as ETP-ALL, near ETP-ALL, cortical T-ALL and medullary T-ALL. Clinical details were retrieved from patient case files. Results: Patient age ranged from 1 to 64 years. Male to female ratio was 2.1: 1 and 35.1% cases were documented to have 3 mediastinal mass. Mean haemoglobin level was 8.6 g/dl, and median total WBC count was 118.3 × 10/µl. Blast percentage ranged from 39-98%, with mean of 84.8%. On flow cytometry analysis, all cases expressed CD7 and cytoplasmic CD3. CALLA+ (CD10+) were 32.4% cases. The aberrant expression of B-cell marker (CD79a) was observed in 5.4% cases. Majority of the cases were classified as medullary T-ALL, constituting 37.8% cases. ETP-ALL were 21.6% cases, 13.5% cases were near ETP-ALL and 24.3% cases were cortical T-ALL. One case could not be definitely assigned to a specific category. Conclusion: This study reflects the difficulties encountered in subtyping of T-ALL cases due to antigenic overlap and/or due to lack of an extended panel of secondary markers.