Abstract Introduction Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms that were historically described as solitary mesotheliomas of the pleura. Although initially recognized as pleural in origin, they can arise in a wide range of extrapleural sites. Intrapulmonary SFTs, however, are exceedingly uncommon. Case Presentation A 67-year-old Asian man with Neurofibromatosis type 1 (NF1) was incidentally found to have an enlarging ovoid pulmonary nodule with coarse calcifications in the right lower lobe during trauma workup. The lesion measured 11 mm, having increased from 7 mm over three years. A follow-up PET scan showed no metabolic activity, and the nodule was presumed to be a hamartoma and kept under surveillance. Over the subsequent four years, annual imaging demonstrated gradual enlargement to 14 × 11 mm, 14 × 13 mm, and finally 18 × 15 mm, with no other radiologic changes over six years. Given the persistent growth, a biopsy was performed to determine whether the lesion represented an enlarging benign or malignant tumor, or a neurofibroma. Fine-needle aspiration (FNA) revealed a spindle cell neoplasm with strong STAT6 expression confirming diagnosis of solitary fibrous tumor. The patient subsequently underwent a wedge resection, which confirmed an SFT with focal ossifications, and a Ki-67 index 5% classifying it as low risk solitary fibrous tumor according to the Demicco Risk Model ( 10% risk chance of metastasis). Discussion SFTs are typically benign, though malignant and metastatic variants have been reported. They are classically pleural in origin, with rare cases showing extension into adjacent lung parenchyma. Due to the nature of histology, intrapulmonary SFTs are theorized to either arise directly from the fibroblasts in the pulmonary parenchyma or as a consequence of intrapulmonary fibrosis in the region where the connective tissue of the interlobular septa and subpleural mesenchyma meet. There are no radiographic pathognomonic features; however, hypermetabolic activity on PET is often suggestive of malignancy 3.Histopathologic examination remains the diagnostic gold standard. Although both neurofibromas and SFTs consist of spindle cells, they are histologically distinct; SFTs are negative for S100 staining. There is no known association between NF1 and SFTs. The overall prognosis of intrapulmonary SFTs is favorable. Complete surgical resection remains the treatment of choice and is generally curative. Conclusion This case highlights that intrapulmonary solitary fibrous tumors, although rare, can occur in patients with Neurofibromatosis type 1. While the coexistence may be incidental, it raises the possibility of a broader mesenchymal tumor predisposition in NF1 that warrants further investigation. This abstract is funded by: na
Ashraf et al. (Fri,) studied this question.