The Silent Intruder: A Case Report of an Incidentally Discovered Solitary Fibrous Tumor of the Lung.

Solitary fibrous tumors (SFTs) are rare fibroblastic mesenchymal neoplasms with a predominantly benign, indolent course and low metastatic potential. Although SFTs most commonly arise within the pleura of the thoracic cavity, primary intrapulmonary origin, wherein the tumor arises within the lung parenchyma itself rather than the pleural surface, represents an exceptionally rare and diagnostically challenging clinical entity. Here, we present the case of an 80-year-old man with an incidentally discovered SFT in the left lung during an active tuberculosis (TB) rule-out due to a positive QuantiFERON-TB Gold test performed as part of a mandatory screening protocol upon enrollment as a new nursing home resident. The review of systems was negative, and the physical examination was unremarkable except for decreased breath sounds in the left lower lung field. Chest X-ray demonstrated an ovoid left lung mass measuring approximately 14 cm in diameter, subsequently confirmed on CT as a 12.5 × 10.4 × 6.5 cm well-demarcated soft tissue tumor in the left lower lobe. The diagnosis was confirmed by histopathologic examination and immunohistochemistry (IHC) of a biopsy specimen from the left lung mass, which demonstrated characteristic spindle cell morphology with STAT6 and CD34 nuclear positivity. The patient was referred to hematology oncology for further management and subsequently underwent complete surgical resection via video-assisted thoracoscopic surgery. This case expands the clinicopathological spectrum of primary intrapulmonary SFTs, demonstrating that atypical presentations may remain clinically silent yet be identified through systematic radiological evaluation. Surgical resection with long-term surveillance remains essential, and prospective multicenter studies are warranted to develop guidelines specific to this rare entity.