Advanced Gastric Adenocarcinoma Presenting With Shoulder Pain and Diplopia

Gastric adenocarcinoma is a leading cause of cancer-related mortality worldwide, with many cases diagnosed at an advanced stage. While liver, peritoneal, and lymphatic involvement are common, metastases to soft tissue and orbital structures are exceedingly rare and may present with non-specific symptoms that mimic benign conditions. We report the case of a 48-year-old woman who presented with persistent musculoskeletal pain and diplopia. Initial symptoms were attributed to sciatica, but further evaluation revealed a right orbital mass, gastric antral thickening, peritoneal carcinomatosis, and multiple soft tissue metastases. Biopsy of the gastric lesion confirmed high-grade, poorly differentiated adenocarcinoma, microsatellite stable, and negative for HER2 and PD-L1 expression. The patient received palliative stereotactic radiation therapy to the orbit and systemic chemotherapy with FOLFOX. Although her symptoms initially improved, she experienced multiple complications, including bacteremia, gastrointestinal bleeding, and thromboembolic events, ultimately leading to a transition to comfort-focused care. This case highlights the importance of maintaining a broad differential diagnosis in patients with persistent or atypical symptoms and underscores the need for early imaging and multidisciplinary evaluation. Recognition of rare metastatic patterns in gastric cancer is essential to avoid diagnostic delays and initiate appropriate treatment strategies that can improve quality of life, even in the setting of advanced disease.