PITFALLS IN THE HISTOPATHOLOGICAL DIAGNOSIS OF SCLEROSING RHABDOMYOSARCOMA

Rhabdomyosarcoma (RMS) is the most common soft tissue malignancy occurring in childhood and adolescence. RMS was previously classified into the following three main subtypes: embryonal, alveolar, and pleomorphic. In the latest classification, a new variant of RMS, spindle/sclerosing RMS, has been included. This variant is rare, occurring in 5%-10% of all cases of RMS. It is characterized by prominent hyaline and sclerosis stroma that mimics an osteoid or chondroid with a pseudovascular, microalveolar, or cord growth pattern. Therefore, it might be easily mistaken during initial evaluation as osteosarcoma, chondrosarcoma, angiosarcoma, infiltrating carcinoma, spindle cell sarcoma, or other RMS types. Awareness of the existence of this entity is important for not only diagnosis but also prognosis and treatment. Here we present the case of a child with sclerosing RMS that was not easily diagnosed. This report aims to discuss the potential diagnostic pitfalls associated with other look-alike sarcomas.