An 84-year-old Japanese woman visited our hospital because of a right intrathoracic tumour that was discovered on routine chest radiography. The patient presented no symptoms, family history of malignancy, or genetic disease. The patient’s medical history included hypertension, stroke, and mild dementia.
On blood examination, serum tumour markers exhibited mild increases in cytokeratin-19 fragment [6.1 ng/mL (<3.5 ng/mL)] and progastrin-releasing peptide [112.4 pg/mL (≦80.0 pg/mL)] levels; however, carcinoembryonic antigen and squamous cell carcinoma-related antigen levels were in normal range.
On radiological examination, chest computed tomography (CT) performed 3 years prior revealed no abnormalities. A recent chest roentgenogram (Figure 1A) and computed tomography (CT) scan (Figure 1B) revealed a large 8-cm mass in the right lower pulmonary lobe that was considered lung cancer invading the ribs and intercostal muscles. For differential diagnosis, chest wall tumours invading the right lung, such as solitary fibrous tumours (SFTs) and desmoid fibromatosis, were considered. CT-guided needle biopsy was performed (Figure 1C); nevertheless, it was difficult to determine whether it was a tumour- or non-tumour-based cancer because it predominantly comprised mature, slightly glassy fibrotic tissue.
Preoperative 18F-fluorodeoxyglucose (FDG) positron emission tomography revealed an abnormal FDG uptake (maximum standardized uptake value =7.2), consistent with the edge of this mass (Figure 1D).
Although undiagnosed, a large 8-cm mass developed over 3 years, and it was considered highly malignant based on its clinical course; thus, surgery was performed for diagnosis and treatment.
Intraoperatively, a large 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 (Figure 2A). Right lower lobectomy and combined resection of the sixth–eighth ribs were performed (Figures 2B, 2C, 2D, and 2E). A separate tumour nodule was identified in the pleura near the tumour (Figure 2C) and resected along with the adjacent parietal pleura. A posterolateral thoracotomy of 25 cm was required for this procedure (Figure 2F).
Grossly, the resected mass measured 8.0 x 7.7 x 6.0 cm. The cut surface was white, and the tumour’s interior seemed to be degenerated (Figure 3A). The tumour extended across the chest wall and lung.
Microscopically, cellularity varied in different areas of the same tumour. The tumour comprised bland-appearing spindle cells. Nuclear pleomorphism was slight (Figure 3B). The pleura was detected between the tumour and the lung, and the tumour was considered to have originated from the pleura. Immunohistochemically, the tumour was positive for MUC4 (Figure 3C); focally positive for alfa-SMA (Figure 3D); and negative for CD34, STAT6, and β-catenin. The MIB1 index was 5–10%. Based on the histomorphological and immunohistological findings, the final diagnosis was LGFMS originating from the chest wall.
FISH analysis of the resected tumor confirmed the presence of a translocation of the FUS gene responsible for LGFMS (Figure 4). The postoperative course was uneventful, the patient was discharged on the 13th postoperative day. The patient has been well for 7 months since surgery.