P2095 - Not All That Stains Gastric Is Gastric: When Histology Tells the Wrong Story

Tooba Laeeq, MD, Yassin Naga, MD, Jose Aponte-Pieras, MD
Kirk Kerkorian School of Medicine at the University of Nevada Las Vegas, Las Vegas, NV

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 female with PMH of stage 4 breast cancer on chemotherapy and immunotherapy (with metastasis to brain, liver, lung, and bone), hypothyroidism, and bilateral upper extremity DVT on Eliquis presented with hematemesis and abdominal pain. She reported nausea and epigastric pain preceding hematemesis. The patient reported three episodes of hematemesis, each a cup in volume, and one episode of melena. Laboratory data revealed hemoglobin 8.7, MCV 100.7, WBC 6.36, platelets 92, albumin 2.3, total bilirubin 1.4, alkaline phosphatase 534, AST 132, ALT 18, INR 2.08, PTT 47. CT abdomen and pelvis with IV 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. EGD 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.

Disclosures:
Tooba Laeeq indicated no relevant financial relationships.
Yassin Naga indicated no relevant financial relationships.
Jose Aponte-Pieras indicated no relevant financial relationships.

Tooba Laeeq, MD, Yassin Naga, MD, Jose Aponte-Pieras, MD. P2095 - Not All That Stains Gastric Is Gastric: When Histology Tells the Wrong Story, ACG 2025 Annual Scientific Meeting Abstracts. Phoenix, AZ: American College of Gastroenterology.