Abstract
Soft-tissue sarcoma (STS) is a rare malignancy that accounts for less than 1% of all cancers, and recent advances in molecular biology have led to its classification based on genomic information. Some RET-rearranged neoplasms have been reported to present pathological features similar to Neurotrophic Tyrosine Kinase Receptor-rearranged spindle cell neoplasms. Here, we report the first case of head and neck spindle cell sarcoma with a GOLGA5-RET fusion that demonstrated a sustained clinical response to selpercatinib, identified through targeted next-generation sequencing (NGS). The patient was a 43 year-old man with a tumor in the arytenoid region that was resected and diagnosed as a malignant spindle cell tumor. Despite initial treatment with surgical resection alone, local recurrence was confirmed, requiring salvage therapy with total laryngectomy and bilateral cervical dissection. Surgical specimen revealed a spindle tumor with a patternless pattern and collagenous stroma. Immunohistochemistry (IHC) with positivity for CD34, bcl-2 (focally), S100, and weak nuclear staining for STAT6, with absence of expression of CK AE1/3, desmin, c-kit, smooth muscle actin, myogenin, synaptophysin, and SOX10. Trk A/B/C were also negative on IHC. Following confirmation of multiple lung metastases, the patient was treated with doxorubicin monotherapy. Targeted NGS identified GOLGA5-RET rearrangement, FGF14 amplification (equivocal), CDKN2B loss, and CDKN2A loss. GOLGA5-RET rearrangements were validated through fluorescence in situ hybridization. The patient subsequently was enrolled in a phase 1/2 trial for the selective RET inhibitor selpercatinib, resulting in a sustained partial response over 5 years. Although solitary fibrous tumor (SFT) was initially considered as a differential diagnosis based on immunohistochemical findings, the lack of strong and diffuse STAT6 expression made this diagnosis unlikely. Subsequent next-generation sequencing (NGS) revealed a RET fusion, leading to the diagnosis of an RET-rearranged spindle cell neoplasm. This case highlights the importance of genomic testing for certain spindle cell sarcomas and the potential benefit of RET-specific inhibitors against RET-altered sarcomas.