Primary Bone Leiomyosarcoma in Neurofibromatosis Type 1: Extremely Rare Concurrency.

Neurofibromatosis type 1 (NF1) is a complex autosomal dominant, multisystem genetic disease affecting about 1 in 3500 individuals. Plexiform neurofibromas represent a rare variant (30%) of NF1 in which the spread of tumor cells along nerve fascicles leads to a diffuse mass of thickened nerve fibers. Affected patients with NF1 have a greater chance of developing soft tissue sarcomas than the general population. Leiomyosarcoma is one of the most frequent soft tissue sarcomas, seldom observed in patients with NF1. Herein we report a rare concurrency of bone leiomyosarcoma in a patient with a plexiform neurofibroma, adding to the few reported cases of leiomyosarcomas in patients with NF1. Our case is a 14-year-old male who is a known case of NF1 and presented with a four-month history of pain and swelling on the medial side of the right knee. Imaging and biopsy confirmed the diagnosis of leiomyosarcoma. Based on the authors' knowledge and search, this is the first reported case of plexiform neurofibroma with a primary bone leiomyosarcoma, representing an extremely rare concurrency. Patients with such uncommon tumors should be assessed regularly, and continuous follow-up is essential.