由于罕见、显微镜特征有很大重叠且免疫组化检测常常具有非特异性，许多软组织肿瘤的分类仍然主观。运用分子遗传学工具，利用这些肿瘤深层次的分子发病机制，显著改善了病理学家的诊断能力，并通过客观的分子标记细化了分类。本研究描述了在国际合作中，在选定的84个罕见的、大多数不可分类的间叶性肿瘤中，通过3年的实验评估了分子遗传学在肉瘤专家病理学评估中的附加诊断价值，其中74个来源于软组织，10个来源于骨骼。病例组成（71%为历史性，29%为当代性）主要包括罕见而棘手的软组织肿瘤，尽管进行了专家评估和常规辅助方法（包括广谱的免疫组化检测和一定数量的商业可用荧光原位杂交探针）仍然无法进行分类。所有病例都进一步经过荧光原位杂交（FISH）检测，使用广泛的自定义人工染色体探针，覆盖肉瘤中已知融合的大部分区域，同时在13个FISH阴性病例中进行靶向RNA测序，以发现潜在的新融合基因。48/84个肿瘤（57%）发现了定义肿瘤的分子变化。在27例（32%）病例中，通过附加的分子工作诊断被细化或修订，其中5例病例（6%）的更新诊断具有临床意义。由于这些肿瘤的分子表征变得越来越多，肉瘤分类正在快速发展，因此，毫不奇怪，本系列肿瘤中有17%仅最近才被描述为定义新的分子定义的软组织肿瘤亚群。© 2023 Wiley Periodicals LLC.

The classification of many soft tissue tumors remains subjective due their rarity, significant overlap in microscopic features and often a non-specific immunohistochemical (IHC) profile. The application of molecular genetic tools, which leverage the underlying molecular pathogenesis of these neoplasms, have considerably improved the diagnostic abilities of pathologists and refined classification based on objective molecular markers. In this study, we describe the results of an international collaboration conducted over a 3-year period, assessing the added diagnostic value of applying molecular genetics to sarcoma expert pathologic review in a selected series of 84 uncommon, mostly unclassifiable mesenchymal tumors, 74 of which originated in soft tissues and 10 in bone. The case mix (71% historical, 29% contemporary) included mostly unusual and challenging soft tissue tumors, which remained unclassified even with the benefit of expert review and routine ancillary methods, including broad IHC panels and a limited number of commercially available fluorescence in situ hybridization (FISH) probes. All cases were further tested by FISH using a wide range of custom bacterial artificial chromosome probes covering most of known fusions in sarcomas, whereas targeted RNA sequencing was performed in 13 cases negative by FISH, for potential discovery of novel fusion genes. Tumor-defining molecular alterations were found in 48/84 tumors (57%). In 27 (32%) cases the tumor diagnosis was refined or revised by the additional molecular work-up, including five cases (6%), in which the updated diagnosis had clinical implications. Sarcoma classification is rapidly evolving due to an increased molecular characterization of these neoplasms, so unsurprisingly 17% of the tumors in this series harbored abnormalities only very recently described as defining novel molecularly defined soft tissue tumor subsets.© 2023 Wiley Periodicals LLC.