[Immunophenotypic Features and Clinical Prognosis of Patients with Mixed Phenotype Acute Leukemia].

Objective: To retrospectively analyze the laborotary test results and clinical data of 31 patients with mixed phenotype acute leukemia (MPAL) in order to summarize and discuss the biological characteristics, curative effect, and prognosis of each subtype of MPAL based on immunophenotype results.

Methods: MPAL patients diagnosed and treated in our hospital from July 2013 to January 2019 were selected to analyze the data of cell morphology, immunophenotyping, cytogenetics, molecular biology (MICM), and routine blood at initial diagnosis. Follow-up was carried out until the last discharge time.

Results: Among 31 patients, there were 19 males and 12 females, with a median age of 41(12-76) years old. According to the results of immunophenotyping and EGIL score, there were 16 cases of myeloid-T lymphoid mixed phenotype (myeloid-T group), 9 cases of myeloid-B lymphoid mixed phenotype (myeloid-B group), 5 cases of T-B lymphoid mixed phenotype (T-B group), and 1 case of myeloid-T-B lymphoid mixed phenotype. Compared between different subtypes, the antigen expression characteristics were the highest positive rate and expression rate of HLA-DR in myeloid-B group, and the positive rate of CD2 in T-B group was significantly higher than that in the myeloid-T group. Meanwhile, the expression rates of CD7 and cCD3 (cytoplasmic CD3) in T-B group were higher than those in myeloid-T group, and cCD79a was positive in all cases of myeloid-B group and T-B group. The median WBC of T-B group was 81.92×10⁹/L, which was significantly higher than that of the other two groups (P<0.05). The quantitative results of WT1 were higher than 10^-4 in 92.6% of the patients, and the WT1 expression level in myeloid-B group was significantly lower than the other two groups (P<0.01). Among the 9 patients with myeloid-B mixed phenotype, 5 cases showed BCR-ABL positive. Among 28 patients followed up, 21 cases achieved complete remission (CR), the median time to first obtain CR was 32.5(9-75) days, and the median follow-up time was 16 months (range from 21 days to 6 years). The CR rate and median overall survival (OS) time in myeloid-B group were 88.9% and 40 months, which were higher than the other two groups. The CR rate and 3-year OS rate in T-B group were relatively lower (50.0%, 0).

Conclusion: WT1 gene is highly expressed in patients with MPAL, and each subgroup of MPAL based on immuophenotype has its unique antigen expression characteristics. Compared with myeloid-T group and T-B group, myeloid-B group can acquire higher remission rate and have better prognosis.