Solitary Fibrous Tumor Arising in Thyroid Follicular Nodular Disease: A Case Report

Herein, we present the first documented case of a solitary fibrous tumor (SFT) arising within thyroid follicular nodular disease and discuss its histogenesis.

A man in his 60s presented with a left thyroid nodule. Histologically, the nodule was composed of spindle cells and thyroid follicles. The spindle cells were positive for CD34 and STAT6, negative for PAX8 and cytokeratin, and harbored a NAB2::STAT6 fusion, confirming the diagnosis of SFT. No extrathyroidal SFT was identified, and the Demicco model classified the tumor as low risk.

This report suggests that SFT may arise de novo within the stromal component of thyroid follicular nodular disease. This underscores the need to consider SFT in the differential diagnosis of spindle-cell lesions occurring within thyroid nodules.