A 45 year old man presented with abdominal pain and anemia. He was found to have a 6 cm ulcerated mass in the small bowel, extending into the mesentery. The tumor was initially thought to represent a GIST. The patient developed liver metastases 2 years later and then multiple bone metastases 4 years after the time of primary diagnosis.

The tumor has a biphasic appearance. In the superficial submucosal aspect of the lesion, the tumor consists of rounded cells with limited amounts of clear cytoplasm (or perhaps clear perinuclear retraction artefact), associated with dense hyaline stromal collagen. In areas, these cells are arranged in cords and strands. The nuclei are quite uniform and show only infrequent mitotic figures. Other areas of the tumour, mainly located deeper in the intestinal wall, have spindle cell morphology, consisting of cells with tapering nuclei and indistinct cytoplasm arranged in whorls within a variably myxoid or collagenous stroma. The subsequent biopsies obtained from both liver and spine consisted of tumor composed of rounded epithelioid cells with clear cytoplasm distributed in a prominent hyaline collagenous stroma. Immunohistochemistry demonstrated multifocal positivity for EMA and diffuse strong positivity for MUC4, while stains for S-100 protein, desmin, c-kit and DOG-1 were negative.

HYBRID SCLEROSING EPITHELIOID FIBROSARCOMA / LOW-GRADE FIBROMYXOID SARCOMA