Solitary Fibrous Tumor of the Uterus Presenting With Lung Metastases: A Case Report.

We describe the case of an 81-yr-old woman who presented with bilateral pulmonary nodules in the setting of a large uterine mass, concerning for a gynecologic malignancy such as leiomyosarcoma. However, fine-needle aspiration of a lung nodule revealed a spindle cell neoplasm consistent with solitary fibrous tumor (SFT), a rare mesenchymal neoplasm characterized by a patternless architecture of spindle cells and branching ectatic vessels. Total abdominal hysterectomy demonstrated a primary SFT of the uterus. Both the lung lesion and uterine mass were positive for STAT6, a sensitive and specific biomarker for SFT. SFT infrequently metastasizes and only rarely occurs in the uterus. These tumors are considered to have uncertain malignant potential, and the diagnosis of "malignant" SFT requires the presence of >4 mitoses per 10 high-power fields. The uterine SFT we report did not meet this criterion for malignancy, emphasizing that this entity can behave aggressively even without increased mitoses or atypical histology. To our knowledge, this is the first reported case of a uterine SFT with metastasis to the lung. We discuss the differential diagnosis for the finding of multiple pulmonary spindle cell lesions in the setting of a uterine mass.