Introduction: While uterine leiomyosarcoma, an aggressive smooth muscle malignancy, has a strong propensity for hematogenous spread—most commonly to the lungs and liver—gastric metastasis remains exceedingly rare. When it occurs, it presents as a masquerading lesion that mimics primary gastric tumors, creating a significant diagnostic pitfall for both clinicians and pathologists. Case Description: A 75-year-old female presented with recurrent melena. Esophagogastroduodenoscopy revealed a friable, bell-shaped mass measuring 7 × 6 cm in the gastric fundus, suspicious for GIST. Histopathology showed spindle to epithelioid tumor cells arranged in intersecting fascicles and solid sheets with vesicular nuclei, conspicuous nucleoli, numerous mitosis, and tumor necrosis. IHCs demonstrated strong SMA positivity but negative CD117, raising consideration of undifferentiated GIST. However, subsequent DOG1 staining was negative, arguing strongly against GIST. Additional markers including S100, PanCK, CD3, CD20, CD15, and CD30 were negative. Further IHCs revealed diffuse, desmin and H-caldesmon positivity, supporting smooth muscle differentiation. Review of prior records revealed TAHBSO in 2023 for uterine leiomyosarcoma. Discussion: Metastatic involvement of the stomach is rare and most commonly arises from breast or lung primaries. Gastric metastases are rare and most commonly originate from breast or lung primaries. Metastatic uterine leiomyosarcoma presenting as a solitary gastric mass is exceedingly uncommon and may closely mimic primary gastric tumors such as GIST both endoscopically and histologically, representing an important diagnostic pitfall. Conclusion This case highlights a rare metastatic pattern of uterine leiomyosarcoma presenting as an overt gastric mass with GI bleeding. Awareness of this deceptive presentation and careful clinicopathologic correlation are essential for accurate diagnosis. To our knowledge, this represents one of the few reported cases worldwide and possibly the first documented in the Philippines.
Gastrointestinal Stromal Tumors ; Immunohistochemistry ; Leiomyosarcoma ; Gastrointestinal Hemorrhage