Orbital malignant rhabdoid tumor with an aberrant immunophenotype: a case report

Malignant rhabdoid tumor (MRT) is a highly aggressive pediatric neoplasm defined by SMARCB1/INI1 loss, and primary orbital involvement is rare.

A 20-month-old girl presented with rapidly progressive left proptosis. Magnetic resonance imaging demonstrated a 2.1 × 1.3 × 1.6 cm temporal retrobulbar mass with focal bone erosion. The primary tumor was treated with piecemeal excision, followed by adjuvant chemoradiotherapy. Pathology showed large epithelioid tumor cells with rhabdoid morphology. Immunohistochemistry revealed diffuse expression of vimentin, CK, and CD34, but INI1 loss and SALL4 negativity. Fluorescence in situ hybridization confirmed a heterozygous SMARCB1 deletion. However, rapid local progression with extension into the temporal lobe occurred 3 months after completion of the treatment. Salvage therapy led to marked radiographic regression, but was discontinued due to severe cytopenias. The patient died of intracranial progression 34 months after the initial surgery.

Orbital MRT can exhibit an atypical CD34-positive and SALL4-negative immunophenotype. The tumor demonstrates highly aggressive behavior, and adjuvant chemotherapy and radiotherapy may provide only temporary control.