Spindle Cell Neoplasm With a Novel MN1::TAF3 Fusion: A Rare Case in a Toddler

Spindle cell tumors in the pediatric population are uncommonly reported. This case discusses an 18-month-old who presented initially with unilateral ptosis and was found to have an orbital spindle cell tumor. Pathology evaluation of the tissue was extensive with nonspecific morphologic and immunohistochemical features. Molecular testing demonstrated an MN1::TAF3 fusion on RNA sequencing, which has not been previously described in the literature in association with spindle cell neoplasms. This case highlights the challenging nature of classifying and treating a tumor with a novel fusion.