Breast cancer is capable of spreading from the initial site to distant organs, a process known as metastasis. While rare compared to common sites like the bones, lungs, or liver, breast cancer can spread to the stomach. When this distant spread occurs, the disease is classified as metastatic breast cancer (MBC) or Stage IV disease. Clinical studies report a low incidence of metastasis to the stomach, ranging from approximately 0.3% to 6% of cases with distant spread. Autopsy studies suggest a higher frequency, indicating that gastric involvement is sometimes present but not clinically detected.
The Pathway of Metastasis to the Gastrointestinal Tract
The journey of cancer cells from the breast to the stomach involves a specific biological process of dissemination. Cancer cells must first detach from the primary tumor and then invade the circulatory system, typically traveling through the bloodstream or the lymphatic system. Once in the circulation, the cells must survive the body’s immune defenses and successfully exit the vessels in a distant organ to form a new tumor.
The stomach is an uncommon target due to “organ tropism,” where cancer cells favor specific distant organs. The stomach lacks the favorable microenvironment that attracts breast cancer cells to sites like the bones or lungs, making metastasis to the gastrointestinal (GI) tract unusual. When spread to the GI tract occurs, the stomach is the most frequent site, followed by the colon and small intestine.
Gastric metastasis is strongly correlated with Invasive Lobular Carcinoma (ILC). Although ILC accounts for about 10% to 15% of all breast cancers, it is responsible for the vast majority of GI metastases. This subtype is characterized by losing the cell-adhesion protein E-cadherin, allowing cells to detach easily and infiltrate tissues in a single-file pattern.
This nature enables ILC cells to infiltrate the stomach wall in a diffuse, submucosal pattern. This often results in a condition mimicking linitis plastica, where the stomach wall becomes thickened and rigid. The interval between the initial breast cancer diagnosis and gastric metastasis detection is often long, averaging four to ten years, or sometimes decades later. Gastric metastasis is usually part of a widespread systemic disease, often occurring alongside other sites of spread like the bone.
Recognizing Signs of Gastric Involvement
Signs that breast cancer has spread to the stomach are often non-specific, easily mistaken for common gastrointestinal issues or side effects of prior treatments. This vagueness can significantly delay diagnosis, especially since symptoms may appear many years after the initial breast cancer diagnosis.
Patients may experience persistent nausea and vomiting. Abdominal pain or discomfort is frequently reported, along with bloating or fullness. A defining symptom is early satiety, the feeling of being full after eating only a small amount of food, often due to the stiffening of the stomach wall caused by infiltrating cancer cells. Other signs include difficulty swallowing (dysphagia), persistent indigestion (dyspepsia), unexplained weight loss, and anemia, which may result from slow internal bleeding.
Confirming the Diagnosis
Confirming that GI symptoms are caused by metastatic breast cancer requires a comprehensive diagnostic approach, as the presentation can mimic primary stomach cancer. Imaging studies, such as CT or PET scans, identify abnormal thickening in the stomach wall but are not definitive for diagnosis.
The gold standard for confirmation is an upper endoscopy, or esophagogastroduodenoscopy (EGD), which allows direct visual inspection of the stomach lining. During the EGD, tissue samples are taken via biopsy. Because cancer cells often infiltrate the deeper layers beneath the mucosal surface, initial biopsies may miss the tumor, necessitating multiple or deeper samples.
Immunohistochemistry (IHC) staining of the biopsy tissue is essential for differentiating metastatic breast cancer from a primary stomach tumor. This specialized testing checks for markers characteristic of breast cancer cells, such as the hormone receptors (Estrogen Receptor and Progesterone Receptor) and proteins like GATA3 or GCDFP-15.
Treatment Strategies for Metastatic Disease
The presence of breast cancer spread to the stomach signifies Stage IV disease, and treatment is primarily systemic, targeting cancer cells throughout the body. The strategy is highly personalized, depending on the metastatic tumor’s biological characteristics, specifically its hormone receptor and HER2 status.
Since most gastric metastases originate from hormone receptor-positive Invasive Lobular Carcinoma, hormonal therapy is often the first-line option. This approach includes medications like selective estrogen receptor downregulators or aromatase inhibitors, often combined with targeted therapies such as cyclin-dependent kinase 4/6 (CDK4/6) inhibitors.
Chemotherapy is another systemic option, used particularly for hormone receptor-negative tumors or for patients whose cancer has progressed after hormonal treatment. Targeted therapy, such as HER2 inhibitors, is used if the tumor tests positive for the HER2 protein.
Local treatments like surgery or radiation are generally reserved for managing complications, rather than being a primary curative strategy. Surgery may be performed palliatively to relieve severe obstruction or control significant bleeding. The goal of all systemic treatment is to control the disease, manage symptoms, and maintain quality of life, as metastatic disease is currently considered incurable.