S6283 Not All That Stains Gastric Is Gastric: When Histology Tells the Wrong Story

Introduction: Breast cancer metastasis is rare in the gastrointestinal tract. The stomach is the most common site, with a reported incidence of 0.2 to 0.7%. A high degree of suspicion is needed as pathology could demonstrate gastrointestinal origin. However breast cancer metastasis to the stomach should be considered in a patient regardless of treatment status. Case Description/Methods: A 44-year-old woman with prior medical history of stage 4 breast cancer on chemotherapy and immunotherapy (with metastasis to brain, liver, lung, and bone), hypothyroidism, and bilateral upper extremity deep vein thrombosis on apixaban presented with hematemesis and abdominal pain. She reported nausea and epigastric pain preceding hematemesis. The patient reported 3 episodes of hematemesis, each a cup in volume, and 1 episode of melena. Laboratory data revealed hemoglobin 8.7, mean corpuscular volume 100.7, white blood cells 6.36, platelets 92, albumin 2.3, total bilirubin 1.4, alkaline phosphatase 534, aspartate aminotransferase 132, alanine transaminase 18, international normalized ratio 2.08, PTT 47. Computed tomography abdomen and pelvis with intravenous contrast revealed numerous lesions throughout the liver, inguinal lymphadenopathy, pulmonary nodules, and sclerotic bone lesions consistent with metastatic disease. Masses within the lower left breast were likely attributed to the patient's primary breast cancer. Esophagogastroduodenoscopy was performed, revealing a large dark clot on the hard palate that was not removed due to thrombocytopenia. Multiple gastric lesions (approximately 5) were noted in the fundus and gastric body with overlying oozing blood and friability with irrigation. The largest lesion sampled with biopsies was isolated to the distal body, measuring approximately 8 mm in diameter. A pathology report of the gastric mass biopsy revealed adenocarcinoma consistent with gastric/upper gastrointestinal or pancreatic biliary origin despite having widespread metastatic lesions from breast cancer. Discussion: This case emphasizes that breast cancer can metastasize to the stomach, mimicking primary gastric cancer clinically and histologically. These metastases resemble poorly cohesive gastric cancer microscopically. Immunohistochemical staining helps differentiate metastatic breast cancer from primary adenocarcinoma. Estrogen receptor, progesterone receptor, and gross cystic disease fluid protein-15 are typically positive only in metastatic breast cancer. Furthermore, hepatocyte nuclear factor 4A is only expressed in primary breast cancer. In conclusion, it is essential to perform immunohistochemical staining in these patients, which significantly impacts treatment and overall outcome.