Rectal Metastasis from Breast Cancer: A Case Report and Review of Literature.

Introduction: Metastatic spread of breast cancer to the gastrointestinal (GI) tract is very uncommon (<1% of all metastases), but it is disproportionately higher in invasive lobular carcinoma (ILC) compared to invasive ductal carcinoma. Its presentation can mimic primary rectal malignancy, often leading to delayed diagnosis. Case Presentation: We describe a 40-year-old woman with metastatic, hormone receptor-positive classic ILC who developed rectal obstruction 2 years after her breast cancer diagnosis. Initial colonoscopy with superficial biopsies was negative. One year later, pelvic magnetic resonance imaging (MRI) demonstrated smooth, concentric thickening of the rectal wall; repeat biopsies confirmed metastatic lobular carcinoma. Conclusion: This case illustrates the diagnostic challenges posed by rectal metastasis from ILC, especially negative superficial rectal biopsies. Endoscopic and radiologic features often mimic primary rectal pathology, underscoring the importance of deep biopsy and imaging in establishing the diagnosis. New lower-GI symptoms in any breast-cancer survivor, especially one with ILC, should prompt pelvic MRI and deep tissue sampling to exclude metastatic disease if superficial biopsies are negative.