Solitary fibrous tumor (SFT) is a rare fibroblastic neoplasm with potentially malignant behavior that may develop in any anatomic site and may involve the head and neck (H&N) region as well. Although typical SFT has a relatively characteristic morphology, its morphologic spectrum is extraordinarily broad and also includes rare cases with dedifferentiation or transdifferentiation which result in aberrant morphologic and/or immunohistochemical features. However, since virtually all cases are molecularly characterized by NAB2::STAT6 gene fusions, molecular genetic methods or STAT6 immunohistochemistry can be effectively used in confirming the diagnosis. Herein, we report 3 diagnostically challenging H&N SFT cases with an unusual morphology and/or phenotypes closely mimicking other well-known H&N entities. The tumors originated in the oral minor salivary glands, the base of the tongue, and sinonasal tract and closely resembled hyalinizing clear cell carcinoma of the salivary gland, adenocarcinoma not otherwise specified and biphenotypic sinonasal sarcoma, respectively. All cases were positive for cytokeratins, variably expressed S100 protein, showed diffuse nuclear STAT6 positivity, and harbored NAB2::STAT6 gene fusions.

孤立性纤维瘤 (SFT) 是一种罕见的纤维母细胞肿瘤，具有潜在的恶性行为，可能在任何解剖部位发生，也可能累及头颈 (H&N) 区域。虽然典型的SFT具有相对特征性的形态学，但其形态学谱非常广泛，还包括罕见的去分化或转分化病例，导致异常的形态学和/或免疫组织化学特征。然而，由于几乎所有病例的分子特征都是NAB2::STAT6基因融合，因此分子遗传学方法或 STAT6 免疫组织化学可以有效地用于确认诊断。在此，我们报告了 3 例具有诊断挑战性的 H&N SFT 病例，其形态和/或表型异常模仿其他众所周知的 H&N 实体。这些肿瘤起源于口腔小唾液腺、舌根和鼻窦，分别与唾液腺玻璃样变透明细胞癌、未另外指明的腺癌和双表型鼻窦肉瘤非常相似。所有病例的细胞角蛋白均呈阳性，S100 蛋白表达不同，显示弥漫性核 STAT6 阳性，并携带NAB2::STAT6基因融合。