Flow Cytometry in Mature T- and NK-cell Neoplasms: A Retrospective Descriptive Study from a Tertiary Care Cancer Centre in Kerala, India

Introduction: Mature T- and NK-cell Neoplasms (MTNKN) constitute around 12% of all non-Hodgkin lymphomas. They have a variable clinical course, ranging from indolent to highly aggressive tumours. Flow cytometry immunophenotyping is crucial for the diagnosis, staging, and classification of MTNKN. Aim: To determine the frequency, morphologic, and immunophenotypic profile of various subtypes of MTNKN diagnosed by flow cytometry. Materials and Methods: This was a retrospective descriptive study conducted at the Department of Pathology, Regional Cancer Centre, Thiruvananthapuram, Kerala, India. All cases of MTNKN diagnosed by flow cytometry in peripheral blood, bone marrow aspirates, or body fluids from January 1, 2010 to June 30, 2020 (10.5 years duration) at the cancer centre were studied. The morphology of tumour cells and immunophenotype by flow cytometry were analysed. Clinical parameters (lymphadenopathy, hepatosplenomegaly, skin lesions, effusions, B symptoms) and follow-up details, including Progression-free Survival (PFS) and Overall Survival (OS), were also noted. Descriptive statistics for continuous variables and frequencies and percentages for categorical variables were obtained. The Kaplan-Meier method for survival plots was used. Results: Mature T- and NK-cell neoplasms constituted 83 cases. The median age of patients was 56 years. The majority of patients were males (n=49). Adult T-cell Leukaemia/Lymphoma (ATLL) (n=50) constituted the most common subtype, followed by Mycosis fungoides/Sezary syndrome (MF/SS) (n=14), T-cell Large Granular Lymphocytic Leukaemia (T-LGLL) (n=7), T-cell Prolymphocytic Leukaemia (T-PLL) (n=4), Aggressive NK-cell Leukaemia (ANKL) (n=3), Hepatosplenic T-cell Lymphoma (HSTL) (n=3), and Anaplastic Large Cell Lymphoma (ALCL) (n=2). OS and PFS at three years were 22.3% and 16.6%, respectively. Conclusion: Mature T- and NK-cell neoplasms presenting as leukaemia is rare. ATLL was the most common subtype of MTNKN. Flower cells, Sezary cells, and prolymphocytes are useful morphological clues for diagnosis. Immunophenotyping by flow cytometry, along with clinicopathologic correlation, is crucial for the diagnosis and subclassification of MTNKN. All subtypes except T-LGLL show inferior PFS and OS

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