Atypical Vascular Proliferation Secondary to Radiotherapy in a Patient With a History of Synovial Sarcoma

We present the case of a 21-year-old male patient with a history of monophasic synovial sarcoma in his left thigh, which was treated with surgical resection, radiotherapy, and chemotherapy with mesna, doxorubicin, and Ifosfamide (MAI protocol). Approximately six years after the end of the oncological treatment, he presented a nodular, polypoid lesion in the left popliteal region, which was painless and fast growing. Ultimately, the biopsy was consistent with atypical vascular proliferation (AVP). Vascular lesions after radiotherapy include a wide spectrum of pathologies that range from benign lesions such as AVP to malignant ones with very poor prognosis such as angiosarcoma, the distinction between one and the other can be difficult, being the determination rearrangement or amplification of gene c-myc, a key to make an accurate diagnosis in case of doubt.