PTCH1-GLI1 Fusion-Positive Ovarian Tumor: Report of a Unique Case With Response to Tyrosine Kinase Inhibitor Pazopanib.

Recurrent GLI1 gene fusions have been recently described in a subset of soft tissue tumors showing a distinct monotonous epithelioid morphology with a rich capillary network and frequent S100 protein expression. Three different fusion partners-ACTB, MALAT1, and PTCH1-have been reported with the PTCH1-GLI1 fusion from 2 patients only, both with head and neck tumors. Herein, we report for the first time a PTCH1-GLI1 fusion in a primary ovarian tumor from a female patient aged 54 years who presented with a 21-cm right ovarian mass and mesenteric metastasis. The tumor was diagnosed as "favor malignant melanoma" based on histologic examination and extensive immunohistochemistry studies. The patient received 4 cycles of pembrolizumab and 2 cycles of trabectedin but developed multiple metastases. A next-generation sequencing-based assay detected a PTCH1-GLI1 fusion, which led to a revised pathologic diagnosis and a change of the patient's management. The patient was switched to the tyrosine kinase inhibitor (TKI) pazopanib to target the sonic hedgehog pathway. Her disease was stable 49 months post TKI therapy. Our case report is the first to show that a tumor with GLI1 oncogenic activation was sensitive to a TKI. The morphologic and immunohistochemistry similarities of our patient's tumor to other recently described tumors harboring GLI1 fusions suggest that these tumors may all belong to the same entity of GLI1 fusion-positive neoplasms and may be treated similarly.