A 47-year-old female with neurofibromatosis type 1 visited our hospital. Physical examination revealed an elastic, hard, rapidly growing mass associated with a reddish skin color change on her back (Fig. 1). Magnetic resonance imaging demonstrated a protruding subcutaneous tumor, 20 × 23 × 14 cm in size, accompanied by direct invasion into the thoracic vertebrae (Fig. 2A: sagittal image; Fig 2B: axial image). A needle biopsy of the tumor revealed features consistent with a malignant peripheral nerve sheath tumor (MPNST). Computed tomography also showed multiple pulmonary metastases. Considering the huge tumor burden and anticipated symptoms in the future, the patient underwent palliative resection of the tumor in her back, including part of the bilateral scapula and spinous processes of the thoracic vertebrae following induction radiotherapy of 30 Gy in 15 sessions. In addition, a bilateral pedicled latissimus dorsi muscle flap and a skin graft were transplanted to cover the musculocutaneous defect in the posterior chest wall.

Pathological examination of the tumor confirmed the diagnosis of MPNST with heterologous rhabdomyoplastic differentiation arising from neurofibroma. To the best of our knowledge, an MPNST exhibiting such a huge tumor has not been reported before. The patient is now under consideration for adjuvant chemotherapy for the pulmonary metastases.