Late Retroperitoneal Metastasis from Invasive Ductal Carcinoma of the Breast: Diagnostic Challenges and the Role of Biopsy and Immunohistochemical Profiling — A Case Report

Abstract

Invasive ductal carcinoma (IDC) is the most prevalent invasive breast cancer. Breast cancer metastasis displays varied patterns and occurs in several organs, with rare occurrence in some regions, including the gastrointestinal system and retroperitoneum. The symptoms of breast cancer metastasis are always nonspecific. Here, we present a female case of retroperitoneal metastasis from IDC involving the cecum and terminal ileum with a late diagnosis. The patient is a 48-year-old female diagnosed with right breast IDC who received neoadjuvant chemotherapy. She subsequently underwent a right modified radical mastectomy with right axillary dissection, followed by adjuvant endocrine therapy and adjuvant radiation therapy. She maintained regular clinical follow-up. Surveillance imaging then detected a possible local recurrence and a retroperitoneal mass invading the cecum that could be another primary. The biopsy from the right chest wall confirmed a recurrence of luminal B breast cancer, but the patient lost follow-up. In February 2025, the patient presented to the ER with a picture of small bowel obstruction (SBO) with other non-specific symptoms. The CT revealed that SBO was secondary to the locally invasive retroperitoneal mass that invaded the cecum and terminal ileum. The peritoneal biopsy was performed, and the histopathology report revealed infiltrative malignant cells with an immune profile consistent with metastatic carcinoma of mammary origin. Therefore, retroperitoneal metastasis from IDC can occur, although this is an unusual location for it. Furthermore, diagnosis of this metastasis after a long time of breast cancer surgery and therapy is a rare condition. Cross-sectional imaging, particularly CT, plays a crucial role in identifying unusual metastatic sites, while histopathological confirmation is necessary to determine the metastatic origin..