A 23-year-old man with a history of Crohn's disease and liver transplantation for sclerosing cholangitis developed pancytopenia during corticosteroid therapy. His blood count showed hemoglobin concentration 81 g/L, white cell count 7.1 × 10⁹/L, neutrophils 0.7 × 10⁹/L, and platelets 34 × 10⁹/L. His blood film showed a population of medium sized lymphoid cells with a high nucleocytoplasmic ratio, some with prominent nucleoli and vacuolation (top left, all images ×100 objective). A large population of these cells were noted in the bone marrow aspirate (top center) and trephine biopsy sections (top right). Immunophenotyping of the CD45^weak cells (purple events plot 1) showed these cells to express CD19, CD79a (plot 2), CD22, HLA-DR, and CD15 (plot 3). Importantly, CD34, CD117, myeloperoxidase, CD10, cytoplasmic CD3, CD79b, and terminal deoxynucleotidyl transferase (TdT) (plot 4), were not expressed, nor was cytoplasmic or surface membrane immunoglobulin (Ig).

The morphology in this case is indicative of a precursor neoplasm and B lineage was indicated by expression of CD19, CD79a, and CD22. Unusually CD34 and TdT were not expressed. The lack of surface and cytoplasmic Ig, weak CD45, absent CD79b and aberrant expression of CD15 are, however, all features of a precursor B-cell neoplasm. Pro-B acute lymphoblastic leukemia, despite arising from an early precursor, may fail to express TdT and sometimes CD34.¹ It is often associated with a KMT2A translocation and this was shown in this case with t(4;11)(q21;q23.3) confirming the diagnosis. Furthermore, the glucocorticoid therapy used in the management of Crohn's disease in this patient may have induced downregulation of precursor antigen expression similar to that reported during induction chemotherapy.^{2, 3}

一名 23 岁男性，患有克罗恩病并因硬化性胆管炎进行肝移植，在皮质类固醇治疗期间出现全血细胞减少症。血细胞计数显示血红蛋白浓度81 g/L，白细胞计数7.1×10 ⁹ /L，中性粒细胞计数0.7×10 ⁹ /L，血小板计数34×10 ⁹ /L。他的血涂片显示一群中等大小的淋巴细胞，核质比较高，其中一些具有明显的核仁和空泡（左上，所有图像×100物镜）。在骨髓抽吸物（上中）和环锯活检切片（右上）中发现大量这些细胞。 CD45^弱细胞的免疫表型分析（紫色事件图 1）显示这些细胞表达 CD19、CD79a（图 2）、CD22、HLA-DR 和 CD15（图 3）。重要的是，CD34、CD117、髓过氧化物酶、CD10、细胞质 CD3、CD79b 和末端脱氧核苷酸转移酶 (TdT)（图 4）不表达，细胞质或表面膜免疫球蛋白 (Ig) 也不表达。

本例中的形态表明前体肿瘤，并且 CD19、CD79a 和 CD22 的表达表明 B 谱系。异常的是 CD34 和 TdT 不表达。然而，表面和细胞质 Ig 的缺乏、CD45 较弱、CD79b 缺失以及 CD15 的异常表达是前体 B 细胞肿瘤的所有特征。 Pro-B 急性淋巴细胞白血病尽管起源于早期前体，但可能无法表达 TdT，有时也无法表达 CD34。¹它通常与KMT2A易位相关，本例中的 t(4;11)(q21;q23.3) 证实了这一点。此外，用于治疗该患者克罗恩病的糖皮质激素疗法可能诱导了前体抗原表达的下调，类似于诱导化疗期间报道的情况。^{2, 3}