Objective: To investigate the clinicopathological features, immunophenotypes, and molecular characteristics of PRRX1-rearranged fibroblastic tumor and to discuss their differential diagnoses. Methods: Four cases of PRRX1-rearranged fibroblastic tumor retrieved from Anning First People's Hospital and Fudan University Shanghai Cancer Center and their clinicopathological features, immunophenotypes and molecular profiles were analyzed. The literature was reviewed. Results: All 4 cases occurred in adult women with an age of 34(27,41) years. Three tumors occurred in the low extremities and 1 in the trunk. The patients presented with a slowly growing mass or swelling, accompanied by pain in 1 patient. Three tumors were located in the subcutis, and 1 tumor in the intermuscular space. The duration lasted for 6 months to 1 year. Tumor ranged in size from 4.0 to 15.8 cm (mean 7.3 cm). At lower power, the tumors were well circumscribed, showing a multinodular architecture. They were composed of bland ovoid to short spindled cells arranged irregularly with interstitial ropey collagen fibers, and set in a fibrous to fibromyxoid matrix with a close resemblance to low-grade fibromyxoid sarcoma. However, all 4 tumors showed negative staining for MUC4. Two tumors were focally positive for S-100 and SOX10. Apart from vimentin, they were all negative for other immunohistochemical stains including SMA, desmin, CD34, STAT6 and β-catenin. The expression of H3K27Me3 was retained. The proliferative index measured by Ki-67 was less than 5%. RNA-sequencing analysis identified PRRX1::NCOA1 fusions in 3 cases, and PRRX1::KMT2D fusion in 1 case. Subsequent FISH study confirmed NCOA1 rearrangement in 3 cases harboring NCOA1 rearrangement. On follow-up (1-14 months), no patient developed either local recurrence or distant metastasis. Conclusions: PRRX1-rearranged fibroblastic tumor is a novel entity of soft tissue tumor that has a predilection for the trunk and extremities, characterized by PRRX1 gene rearrangement and benign clinical course. Familiarity with its clinicopathological features is helpful in the distinction from low-grade fibromyxoid sarcoma and other spindle cell tumors with overlapping features.
目的： 探讨PRRX1重排纤维母细胞肿瘤的临床病理学特征、免疫表型、分子遗传学改变及鉴别诊断。 方法： 收集2023年1月至2024年6月安宁市第一人民医院和复旦大学附属肿瘤医院诊断的4例PRRX1重排纤维母细胞肿瘤进行回顾性分析，总结其临床资料、组织病理学特征、免疫表型及分子改变，并复习相关文献。 结果： 4例均为成年女性，年龄为34（27，41）岁。3例肿瘤发生于下肢，1例发生于躯干。临床上表现为局部肿块或肿胀，1例伴有疼痛。3例位于皮下，1例位于肌间隙。术前病程6个月至1年。肿瘤最大径4.0~15.8 cm（平均7.3 cm）。低倍镜下，肿瘤境界清楚，略呈多结节状。高倍镜下，肿瘤由不规则束状或交织状排列的短梭形或卵圆形细胞组成，瘤细胞之间可见绳索样胶原纤维，间质呈纤维黏液样，形态上类似低度恶性纤维黏液样肉瘤，但免疫组织化学标记显示，瘤细胞不表达MUC4。2例瘤细胞灶性表达S-100蛋白和SOX10。除波形蛋白外，其他标志物包括平滑肌肌动蛋白、结蛋白、CD34、STAT6和β-catenin等均为阴性。H3K27Me3表达无缺失。Ki-67阳性指数<5%。二代测序（RNA测序）显示，3例具有PRRX1：：NCOA1融合基因，1例具有PRRX1：：KMT2D融合基因。3例加做荧光原位杂交检测均显示NCOA1基因重排。随访1~14个月，4例均无复发或转移。 结论： PRRX1重排纤维母细胞肿瘤是一种好发于躯干和四肢的软组织肿瘤新病种，以具有PRRX1基因重排和良性临床经过为特征。熟悉其临床病理性特点和分子表型有助于与低度恶性纤维黏液样肉瘤等形态相似肿瘤相鉴别。.