Update on Superficial Spindle Cell Mesenchymal Tumors in Children

The diagnosis of cutaneous and subcutaneous spindle cell neoplasms in children is often challenging and has potential therapeutic and prognostic implications. Although correctly diagnosing dermatofibrosarcoma protuberans and infantile fibrosarcoma is paramount, pathologists should not ignore a number of diagnostic pitfalls linked to mostly rare tumors with completely different clinical outcomes. In the last decade, a spectrum of novel entities has been described; information from molecular biology has helped to shape this new landscape for spindle cell tumors. Here, we review the most noteworthy neoplasms in this spectrum, with a focus on their histological similarities: fibroblastic connective tissue nevus, medallion-like dermal dendrocyte hamartoma, or plaque-like CD34-positive dermal fibroma, which share features with fibrous hamartoma of infancy; lipofibromatosis and lipofibromatosis-like neural tumor; and plexiform myofibroblastoma, a recently described neoplasm that should be distinguished from plexiform fibrohistiocytic tumor. These tumors also have genetic similarities, particularly gene rearrangements involving NTRK3 or NTRK1. These genetic features are not only essential for the differential diagnosis of infantile fibrosarcoma but are also of diagnostic value for lipofibromatosis-like neural tumors. The more recently described RET, RAF1, and BRAF gene fusions are also discussed.

Plexiform fibrohistiocytic tumor. Series of two cases.

Resumen El tumor fibrohistiocítico plexiforme (TFHP) es una neoplasia mesenquimatosa rara de malignidad intermedia, informada por primera vez por Enzinger y Zhang en 1988. Tiene predilección por niños y adultos jóvenes, pero puede ocurrir a cualquier edad. Suele afectar a extremidades superiores y se presenta como una masa indolora de crecimiento lento. Tiene una alta tasa de recurrencia local y la aparición de metástasis es excepcional. Histológicamente, se caracteriza por una masa dérmica o subcutánea mal demarcada con crecimiento plexiforme multinodular y citomorfología fibrohistiocítica. Se requiere una resección quirúrgica completa de la lesión, preferiblemente con márgenes amplios, para prevenir la recurrencia local. Es necesario un seguimiento a largo plazo para detectar cualquier metástasis nodal o pulmonar. Presentamos una serie de dos casos de TFHP que precisaron de ampliación de márgenes quirúrgicos.