Histiocyte-rich rhabdomyoblastic tumor is a recently described skeletal muscle neoplasm of uncertain malignant potential, characterized by slow growth, a fibrous capsule containing peripheral lymphoid aggregates, spindle-to-epithelioid cells with a rhabdomyoblastic immunophenotype, and a dense histiocytic infiltrate. It most commonly arises within the muscles of the lower legs and trunk in young-to-middle–aged men, and initial reports suggest indolent behavior. In this paper, we present two additional cases of histiocyte-rich rhabdomyoblastic tumor with similar clinicopathologic features and discuss the differential diagnosis including its overlap with inflammatory leiomyosarcoma.

富含组织细胞的横纹肌母细胞瘤是最近描述的具有不确定恶性潜能的骨骼肌肿瘤，其特征是生长缓慢，含有周围淋巴样聚集物的纤维状囊，具有横纹母细胞免疫表型的纺锤体至上皮样细胞以及密集的组织细胞浸润。它最常见于年轻至中年男性的小腿和躯干肌肉内，最初的报道表明行为懒惰。在本文中，我们提出了另外两例具有相似组织病理学特征的富含组织细胞的横纹肌母细胞瘤病例，并讨论了鉴别诊断，包括其与炎性平滑肌肉瘤的重叠。