Fig. 1

Ultrasound imaging reveals a solid, hypoechoic mass with clear boundaries, exhibiting an unevenly thickened pseudocapsule at the margins (A). Tumor is focally encased by fibrous pseudocapsules (B). In myxoid areas, tumor cells exhibit either an epithelioid or spindle-shaped morphology, proliferating in a loosely cohesive reticular or clustered arrangement (C, D). In non-myxoid areas, spindle-shaped tumor cells exhibit bundled growth pattern, forming sheets (E, F). The tumor cells demonstrate focal positivity for MUC1 (G), as well as diffuse positivity for ER (H) and Calponin (I). In contrast, the tumor cells are negative for Keratin (J) and S-100 (K). SMARCB1 expression is completely absent in all tumor cells (L, vascular reactivity used as an internal positive control)