Lynch-Related Metastatic Breast Cancer With Diffuse Gastrointestinal Involvement Diagnosed With Endoscopically Normal Mucosal Biopsies and Endoscopic Ultrasound-Guided Paracentesis

Endoscopic ultrasound-guided paracentesis can safely assist with diagnosis of invasive lobular breast carcinoma after appropriate consideration of infection-related complications. This is a case of metastatic breast cancer presenting without clinical or radiographic breast findings. The patient presented with nonspecific gastrointestinal symptoms with normal endoscopic appearance, but malignant histology. Endoscopic ultrasound-guided paracentesis aided in the diagnosis of metastatic lobular breast carcinoma and can be integrated into the diagnostic armamentarium of advanced endoscopists. In addition, this case highlights an atypical case of Lynch syndrome presenting with index extraintestinal malignancy.