Primary low-grade fibromyxoid sarcoma of the large intestine with lung metastases: A case report and review of the literature

A 70-year old man had multiple lung nodules detected on a computed tomography (CT) performed as part of the work-up for an isolated episode of hematuria of several hours’ duration. A CT-guided lung biopsy disclosed a morphologically undifferentiated neoplasm, that could not be further subclassified despite an extensive immunohistochemical panel. Four years previously the patient had undergone a left hemicolectomy in another institution to resect a 4.7 cm polypoid ulcerated area in the splenic flexure. The slides from that resection were retrieved for review at our institution. There was a variably cellular, diffuse spindle cell neoplastic proliferation involving the submucosa, muscularis propria and subserosa of the large bowel, composed of elongated spindle cells, with small, inconspicuous nucleoli, arranged in intersecting fascicles. Occasional areas of the tumor showed myxoid stroma. Mitotic activity was low. Immunohistochemistry showed strong and diffuse cytoplasmic staining for MUC4 in both the large bowel and lung tumors. Molecular profiling identified a FUS-CREB3L1 fusion gene. The constellation of morphological, immunohistochemical and molecular features are of low-grade fibromyxoid sarcoma (LGFMS) of the large bowel, with metastatic fibromyxoid sarcoma to the lung. LGFMS is a malignant, often late-metastasizing tumor, with a misleadingly bland histological appearance, that typically arises in the deep soft tissues of the proximal extremities or trunk of young adults. Accurate classification, requiring morphology and ancillary tests, is required for appropriate clinical follow-up and treatment of patients. © 2018