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Thymic Immunophenotype, and Expression of CD4 and Myeloid Antigens is Associated with Outcome in Adult Patients with T–Cell Acute Lymphoblastic Leukemia

Areej Al Mugairi, Bakul I Dalal, Steven Pi, Soo Yeon Lee, Nikisha S Khare, Jason Pal, Alok Vakil, Adam Bryant, Sally Lau and Yasser R Abou Mourad

Background: In adult patients with T–cell acute lymphoblastic leukemia (T–aALL), age, WBC count and cytogenetics are used for prognostic stratification. We report the prognostic significance of immunophenotype in T– aALL patients. Methods: We analyzed 27 T–aALL patients treated at the Leukemia-BMT Program of British Columbia between 1989 and 2010 using a standardized protocol for diagnosis, treatment and follow up. The immunophenotyping raw data was re-analyzed to record positivity (≥20% blasts positive), number of blasts positive, and intensity and homogeneity of expression. Thymic phenotype (TP) and expression of myeloid antigens (My+) were defined as any one of CD1a+ or dual expression of CD4 and CD8, and any one of CD13+, CD33+ or CD117+ respectively. Results: Twenty-two (81%) T–aALL patients achieved complete remission (CR); of these, 7(32%) relapsed within 5-22 months (median 15 months). The relapse-free survival (RFS) and overall survival (OS) were 1 -119 (median 18) months and 1-119 (median 25) months respectively. Frequency of CD1a+, CD4+, TP+ and My+ was 58%, 58%, 66% and 50% respectively. Expression of T-cell antigens CD1a, CD4, and TP+ status were favorably associated with outcome: CD1a+ status with OS (p=0.017), CD4+ status with RFS (p=0.015) and OS (p=0.005), TP+ status with CR (p=0.028) and OS (p=0.024). My+ status was adversely associated with CR (p=0.013) and OS (p=0.026). Conclusions: In T–aALL patients, CD1a+, CD4+ and TP+ are favorably, and My+ status are adversely associated with outcome. The percentage of positive blasts and intensity and uniformity of staining for different antigens shows wide variations.