The Value of Sysmex White Precursor Cell Channel in Distinguishing Circulating Large Blastoid Lymphoma Cells from Blasts
Authors: Li Xing , Lin Hua-Fang , Agustin Arnel , Wolgast Lucia , Wang Qing , Shi Yang , Wang Yanhua , Fang Yanan 
Published: October 2024

Abstract

Background
There are rare cases of lymphoma presenting with circulating large blastoid cells mimicking blasts. These abnormal cells usually are medium to large in size with high nucleus-to-cytoplasmic ratio, fine to slightly condensed chromatin, prominent nucleoli, and scant to moderate amount of cytoplasm. Distinguishing them from real blasts is challenging, and although flow cytometry provides a definitive answer, pathologists may feel compelled to offer a quick preliminary assessment to the clinical team, particularly during weekends when flow cytometry is not accessible. We have recently replaced the old CBC instrument with Sysmex XN-9100 which incorporates a new white precursor cell channel (WPC). WPC channel is triggered only when Sysmex differential channels (WDF+WNR) produce a combined flag of “blasts/abnormal lymphocytes?”. The WPC will then separate this into a specific flag for either cell type or remove the flag if it is normal. Our study aims to explore the effectiveness of the WPC Channel in distinguishing blastoid lymphoma cells from true blasts.

Method
Between October 2023 and January 2024, we identified four lymphoma cases exhibiting circulating large blastoid cells. For comparative analysis, we included the most recent seven cases of acute myeloid leukemia (AML) and one case of acute lymphoblastic leukemia (ALL), all featuring medium to large-sized blasts. We collected results from initial testing (WDF+WNR) and WPC reflex testing. The reference for our analysis included manual differentials assisted by CellaVision, pathologist reviews, and immunophenotyping results.

Results
Within four blastoid lymphoma cases, two were diagnosed as blastoid high-grade B-cell lymphomas, one as diffuse large B-cell lymphoma, and another as chronic lymphocytic leukemia with many blast-like cells observed on the cytospin slide (no smear available). Pathologists reviewed the smears and slides of all four cases, categorizing them as blasts or blast-like cells before flow was run. All cases were initially flagged with “Blasts/Abnormal Lymphocyte?” on Sysmex differential channels but were subsequently flagged only with abnormal lymphocytes after the WPC reflex. For comparison, in 7 AML and 1 ALL cases, the WPC channel flagged blasts in 7 out of the 8 cases following the reflex of initial “Blasts/Abnormal Lymphocyte?” flag. The only case flagged with abnormal lymphocytes but not blasts was a case of AML with monocytic differentiation, characterized by many promonocytes and rare blasts.

Conclusion
The WPC channel accurately characterized the challenging large blastoid lymphoma cells as abnormal lymphocytes in all four cases, where morphology characterization was difficult. The study’s limitation lies in its small sample size. We are actively accumulating additional cases with circulating blastoid lymphoma cells, alongside control leukemia cases, to further assess the efficacy of the WPC channel.