成熟 B 细胞急性淋巴细胞白血病 (ALL) 的定义是轻链限制性表面免疫球蛋白 (sIg) 的表达，通常具有伯基特淋巴瘤白血病期的特征，包括 FAB-L3 形态和 MYC 重排。最近，儿童成熟 B 细胞 ALL 中的另一个独特实体被定性为非 L3 形态和 KMT2A 重排。在这里，我们报告了一个不寻常的成熟 B 细胞 ALL 病例，其表现为 RUNX1 重排。一名65岁男性因白细胞增多和血小板减少入院检查。患者骨髓细胞增多，97.8% 髓过氧化物酶阴性、中到大尺寸原始细胞浸润，无细胞质空泡。免疫表型的特征是存在轻链限制性 sIg 且缺乏未成熟标记，表明诊断为具有 L2 形态的成熟 B 细胞 ALL：sIg-κ、CD19、CD20、CD22、CD79a、TdT- 和 CD34- 。 G带结合光谱核型分析显示以下复杂核型：45,X,der(Y;10)(p10;q10),del(13)(q?),inv(21)(p13q22.1)。荧光原位杂交显示21q22.1处RUNX1的分离信号，而未发现MYC和KMT2A的重排。据我们所知，涉及 RUNX1 的 inv(21)(p13q22.1) 是一种新型细胞遗传学畸变，这是首例出现 RUNX1 重排的成熟 B 细胞 ALL 病例。因此，RUNX1 可能与显示非 L3 形态且无 MYC 重排的成熟 B 细胞 ALL 的发病机制有关。

Mature B-cell acute lymphoblastic leukemia (ALL) is defined by the expression of light chain-restricted surface immunoglobulin (sIg) and usually has features of the leukemic phase of Burkitt lymphoma including FAB-L3 morphology and MYC rearrangement. Recently, another distinct entity in childhood mature B-cell ALL has been characterized as non-L3 morphology and KMT2A rearrangement. Here we report an unusual case of mature B-cell ALL that presented with RUNX1 rearrangement. A 65-year-old male was admitted to our department for thorough examination of leukocytosis and thrombocytopenia. The patient's bone marrow was hypercellular and infiltrated with 97.8% myeloperoxidase-negative, medium-to-large-sized blasts without cytoplasmic vacuoles. Immunophenotypes were characterized by the presence of light chain-restricted sIg and the lack of immature markers, indicating a diagnosis of mature B-cell ALL with L2 morphology: sIg-κ+, CD19+, CD20+, CD22+, CD79a+, TdT-, and CD34-. G-banding combined with spectral karyotyping showed the following complex karyotype: 45,X,der(Y;10)(p10;q10),del(13)(q?),inv(21)(p13q22.1). Fluorescence in situ hybridization revealed separated signals of RUNX1 at 21q22.1, whereas rearrangements of MYC and KMT2A were not found. To our knowledge, inv(21)(p13q22.1) involving RUNX1 is a novel cytogenetic aberration and this is the first case of mature B-cell ALL that presented with RUNX1 rearrangement. Thus, RUNX1 may be implicated in the pathogenesis of mature B-cell ALL showing non-L3 morphology without MYC rearrangement.