Navigating diagnostic dilemmas toward precision therapy: a case report and literature review on gastric metastasis from breast cancer

Gastric metastasis from breast cancer (GMBC) is a rare but diagnostically challenging condition, whose clinical and imaging features often mimic primary gastric cancer or treatment-related adverse effects. This study integrates a detailed case of a 54-year-old woman with Luminal B invasive lobular carcinoma who developed gastric metastasis during systemic therapy, with a systematic review of 35 recent cases (2019–2024) to delineate the clinical profile and management of GMBC. In the reported case, immunohistochemical analysis revealed phenotypic evolution, with hormone receptor expression shifting from ER 80%/PR 5% in the primary tumor to ER 30%/PR negative in the gastric metastasis. Literature synthesis identified invasive lobular carcinoma as the predominant histology (57.14%), abdominal pain as the most common symptom (54.29%), and highlighted the diagnostic utility of immunohistochemical markers—particularly GATA3 (positive in 71.43% of tested cases). Treatment remains primarily systemic, with endocrine therapy demonstrating survival benefit in hormone receptor-positive disease. We emphasize the need for heightened clinical suspicion in breast cancer patients with upper gastrointestinal symptoms and propose a structured diagnostic pathway centered on endoscopic deep biopsy and comprehensive immunohistochemical profiling. Re-biopsy to assess phenotypic evolution is crucial for guiding personalized therapy, while surgical intervention should be reserved for palliation of complications or selected cases of oligometastatic disease.