Myeloid sarcoma (MS) is defined as an extramedullary mass-forming lesion composed of immature myeloid cells. It is a rare but well-known manifestation of acute myeloid leukemia. Pediatrics testicular MS may pose a possible diagnostic challenge, an issue that is underscored in the few testicular pediatric MS cases reported in the literature. Herein, we report a series of 5 cases of pediatric testicular MS that are evaluated at the morphologic and immunohistochemical levels with correlation with the KMT2A (MLL) rearrangement status. Three patients presented with no prior history of acute myeloid leukemia. All 5 cases showed monoblastic morphology; positive for CD33, CD43, CD68, CD163, CD4 (dim), and lysozyme; and negative for CD10, CD34, CD117, and myeloperoxidase. KMT2A (MLL) rearrangement was detected in 4 of the 5 cases. In the literature, 8 more cases of pediatric testicular lymphoma were reported. Most of them showed monocytic differentiation and KMT2A (MLL) rearrangement was reported in 3 of the cases. In conclusions, testicular MS in pediatric patients shows monoblastic differentiation which may be attributed to the KMT2A (MLL) rearrangement. We also highlight the importance of using an extended immunohistochemistry panel in the diagnosis of MS.

中文翻译：

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儿童睾丸髓样肉瘤

髓样肉瘤 (MS) 被定义为由未成熟髓样细胞组成的髓外肿块形成病变。这是急性髓系白血病的一种罕见但众所周知的表现。小儿睾丸 MS 可能构成诊断挑战，文献中报道的少数睾丸小儿 MS 病例强调了这一问题。在此，我们报告了一系列 5 例小儿睾丸 MS，这些病例在形态学和免疫组织化学水平上进行了评估，并与 KMT2A (MLL) 重排状态相关。三名患者既往无急性髓系白血病病史。5例均呈单核形态；CD33、CD43、CD68、CD163、CD4（暗淡）和溶菌酶阳性；CD10、CD34、CD117 和髓过氧化物酶阴性。在 5 个病例中的 4 个中检测到 KMT2A (MLL) 重排。在文献中，另有8例小儿睾丸淋巴瘤报告。他们中的大多数表现出单核细胞分化，其中 3 例报告了 KMT2A (MLL) 重排。总之，儿科患者的睾丸 MS 显示出单核细胞分化，这可能归因于 KMT2A (MLL) 重排。我们还强调了在 MS 诊断中使用扩展免疫组织化学面板的重要性。