Subcutaneous Solitary Fibrous Tumor in the Chin of a Young Adult: A Diagnostic Challenge.

BACKGROUND Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms most commonly originating in the pleura but may also arise in extrapleural sites, including the head and neck region. Subcutaneous SFTs in the chin area are exceptionally rare; only a few cases have been reported. CD34 and Bcl-2 are commonly used immunohistochemical markers in the initial diagnostic workup, and their co-expression is strongly suggestive of an SFT. However, CD34 negativity can be misleading and complicate diagnosis. Accurate identification of SFTs is potentially difficult because of histologic variability and overlap with other spindle cell tumors. CASE REPORT We encountered a rare subcutaneous SFT in the chin of a 22-year-old woman who presented with facial asymmetry and a tender mass. Imaging revealed a well-circumscribed, contrast-enhancing lesion in subcutaneous soft tissue over the anterior mandible. Histologically, the tumor lacked typical staghorn vasculature but showed spindle cell proliferation within a fibrous stroma. Immunohistochemistry demonstrated strong nuclear STAT6 positivity; expression of CD99, Bcl-2, and SMA; and focal H-caldesmon staining. CD34, S100, and ALK1 displayed negative staining. Based on these findings, the patient was diagnosed with an SFT. CONCLUSIONS This case highlights the importance of considering SFT in the differential diagnosis of spindle cell tumors in the head and neck region. It also underscores the critical role of immunohistochemistry, particularly STAT6 staining, in distinguishing SFT from histologic mimics. Vigilant follow-up remains essential, especially in atypical or CD34-negative cases, given their potential for aggressive behavior.