Low-grade endometrial stromal sarcoma and ossifying fibromyxoid tumors are two types of mesenchymal tumors that share no similarities in terms of site, sex, and morphological characteristics. They are rare, low grade tumors of uncertain lineage, with no definite immunological markers. Interestingly, a common PHF1 gene- related rearrangement was observed in these two tumors. Here, we report a case of endometrial stromal sarcoma with distinct ossification. Microscopically, the tumor is composed of bland-looking ovoid cells with low cellularity in the fibromyxoid stroma. Foci of metaplastic bone formation were noted. Using a combination of FISH, transcriptome sequencing, and molecular techniques, we identified a new PHF1-BRD8 fusion transcript, which was previously described, but in its reciprocal fusion form. This case expands the current understanding of low-grade endometrial stromal sarcoma and emphasizes the importance of molecular characterization of unique fusion, which may be related to its distinct morphological features and the possibly chemosensitive target.

低级别子宫内膜间质肉瘤和骨化性纤维粘液样肿瘤是两种在部位、性别和形态特征方面没有相似性的间充质肿瘤。它们是罕见的、谱系不确定的低级别肿瘤，没有明确的免疫学标志物。有趣的是，在这两种肿瘤中观察到了常见的PHF1基因相关重排。在这里，我们报告了一例具有明显骨化的子宫内膜间质肉瘤。在显微镜下，肿瘤由纤维粘液样基质中具有低细胞结构的外观平淡的卵形细胞组成。注意到化生骨形成的病灶。结合 FISH、转录组测序和分子技术，我们确定了一个新的PHF1-BRD8融合转录本，之前已经描述过，但是是相互融合的形式。该病例扩展了目前对低级别子宫内膜间质肉瘤的认识，并强调了独特融合的分子特征的重要性，这可能与其独特的形态特征和可能的化学敏感靶点有关。