Histiocyte-rich rhabdomyoblastic tumor: a report of two cases and a review of the differential diagnoses
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BRIEF REPORT
Histiocyte-rich rhabdomyoblastic tumor: a report of two cases and a review of the differential diagnoses Melanine Bourgeau 1 & Anthony P. Martinez 1,2 Received: 29 April 2020 / Revised: 23 May 2020 / Accepted: 28 May 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract 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. Keywords Histiocyte-rich rhabdomyoblastic tumor . Inflammatory leiomyosarcoma . Rhabdomyosarcoma . MyoD1 . Smooth muscle tumors . Rhabdomyoma
Introduction Histiocyte-rich rhabdomyoblastic tumor (HR-RMT) is a recently described skeletal muscle neoplasm of uncertain malignant potential [1]. Martinez et al. identified ten cases of HRRMT, involving the deep soft tissue of the lower extremities, trunk and neck of young-to-middle–aged adults. All cases shared certain characteristics including slow growth, circumscription with surrounding lymphoid aggregates, and a dense intratumoral histiocytic infiltrate, often obscuring the underlying spindle cell rhabdomyoblastic tumor. Atypia was variable but mitotic activity was consistently low (0–1 mitoses/10 HPF). All cases demonstrated diffuse desmin positivity and focal positivity for at least one skeletal muscle marker (myogenin or MyoD1). Several cases underwent molecular testing, and no MyoD1 mutations or gene fusions were identified. Inactivating mutations of NF1 were detected on two of the four cases tested. In the nine patients in whom follow-up
* Anthony P. Martinez [email protected] 1
Department of Pathology and Laboratory Medicine, Emory University, Atlanta, GA 30322, USA
2
Department of Dermatology, Emory University, Atlanta, GA 30322, USA
information was available, all were free of disease, without recurrence or metastasis [1]. Herein, we present two additional cases of HR-RMT and discuss the differential diagnosis in this rare entity as well as its overlap with inflammatory leiomyosarcoma.
Case 1 A 37-year-old male presented with a slowly enlarging mass in his left upper arm that was present “for quite some time” and had been causing him mild pain as well as occasional paresthesia of the arm. Magnetic resonance imaging showed a fusiform circumscribed mass (4.4 × 2.2 × 1.8 cm) within the brachioradialis muscle. The mass demonstrated mild T1 hyperintensity, heterologous T2 hyperintensity, and mostly homogeneous contrast enhancement, with small scattered foci representing cy
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