Low-grade fibromyxoid sarcoma rapidly arising from the chest wall that was difficult to distinguish from lung tumours: A case report

Abstract Background: Low-grade fibromyxoid sarcoma (LGFMS) is a rare mesenchymal tumour, predominantly arising in the limbs and trunks of young adults. This tumour rarely arises in the chest cavity.Case presentation: An 84-year-old Japanese woman visited our hospital because of a right intrathoracic mass that was discovered on routine chest radiography. Based on computed tomography (CT) and 18F-fluorodeoxyglucose positron emission tomography findings, primary lung cancer with chest wall invasion was suspected. Chest CT performed 3 years prior did not reveal any abnormalities. CT-guided needle biopsy did not provide a definitive diagnosis. During the operation, the mass was detected in the right lower lobe of the lung and suspected to have invaded the chest wall directly at the sixth–eighth ribs. Right lower lobectomy and combined resection of the ribs were performed. Microscopically, it was a low-grade spindle cell tumour arising from the pleura and demonstrating focal invasion of the lung. Immunohistochemically, the tumour was positive for MUC4, negative for CD34 and β-catenin, and finally diagnosed as LGFMS. The patient has been well for 5 months after surgery.Conclusions: LGFMS may be histomorphologically diagnosed as a low-grade tumour by needle biopsy; however, in the current case, it was clinically highly malignant because of the appearance of an 8-cm mass over 3 years. Therefore, postoperative, long-term regular medical imaging is recommended, considering the highly malignant nature of the tumour and high risk of local recurrence and pulmonary metastasis.