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60 year old female with a 5.0 cm small bowel mass, biopsy.
Microscopic assessment shows fragments of neoplastic spindle cells with fascicular growth pattern and marked cytologic atypia and pleomorphism. The morphologic features are consistent with a smooth muscle tumour with atypia, favouring leiomyosarcoma.
Leiomyosarcomas (LMS) are malignant smooth muscle tumours that infrequently arise in the gastrointestinal tract. Primary small intestinal LMS show variable behavior and may metastasize into the abdomen and distant sites. The main differential diagnosis includes a GIST, which is more common at this location. Although distinction between these two entities is often straightforward on H&E, a panel of immunohistochemical stains (i.e. smooth muscle markers, CD117 and/or DOG1) may be helpful in problematic cases.
See related content for references:
1) Miettinen M., et al. Am J Surg Pathol. 2009;33(3):430-436