A rare presentation of round cell sarcoma

Undifferentiated round cell sarcomas (URCS) are an extremely rare form of cancer, comprising a heterogeneous group of bone and soft tissue tumors occurring primarily in young adults (but distributed across all ages; range 2mo-81 years) and displaying a slight male predominance. URCS are primarily identified by their genetic abnormalities, with three recurrent oncogenic fusion rearrangements associated in the literature and recently added to the WHO classifications: EWSR1-non-ETS, BCOR-CCNB3, and CIC-DUX4. We present/describe a rare case of an URCS diagnosed in a 27-year-old female following six years of non-specific symptoms including pain and swelling of the third proximal phalanx. This case is only the third reported in a digit and, based on FoundationOne genotyping, was uniquely treated with tamoxifen. This patient also received radiation therapy, surgical resection, and palliative chemotherapy. Metastases were noted in the lungs and mediastinum, and the patient died of disease 89 months after the first treatment. While diagnosis of these tumors is becoming increasingly dependent on molecular profiles, treatment remains mostly unchanged and does not largely reflect the use of genetic results in treatment plans. A comprehensive review of the literature was completed to examine URCS and assist in the development of a diagnostic/treatment algorithm.