# Case Report: Breast metastasis from biliary tract cancer: a rare case and literature review

## TL;DR

A rare case of breast metastasis from biliary tract cancer is reported, emphasizing the importance of accurate diagnosis using pathology and immunohistochemistry.

## Contribution

This case report adds to the limited literature on breast metastasis from biliary tract cancer and highlights diagnostic challenges.

## Key findings

- Breast metastasis from biliary tract cancer can mimic primary breast cancer, requiring detailed pathological analysis.
- Immunohistochemistry was crucial in confirming the biliary origin of the tumor and guiding treatment decisions.

## Abstract

Breast metastasis from biliary tract cancer (BTC) is an extremely rare clinical occurrence. We report the case of a 59-year-old woman who was incidentally found to have a hepatic mass, leading to a comprehensive workup prompted by progressive chest discomfort. Clinical examination revealed a firm left breast with nipple retraction and a palpable axillary mass. Imaging confirmed a non-mass enhancement lesion in the left breast along with extensive metastases to the liver, lungs, bone, and mediastinal lymph nodes. Core needle biopsies of the breast and abdominal wall lesion showed morphologically similar adenocarcinoma. Immunohistochemistry (IHC) was instrumental in the diagnosis, demonstrating positivity for CK19 and IMP3, focal positivity for CDX2, and a high Ki-67 index (80%), while key breast markers (GATA3, ER, PR, and HER2) were all negative. This immunoprofile strongly supported a biliary origin. The patient was diagnosed with advanced BTC with multiple metastases, including to the breast. She received supportive care and was referred for systemic therapy evaluation. This case highlights that BTC breast metastasis can mimic primary breast carcinoma, underscoring the critical role of pathology and IHC in achieving an accurate diagnosis, which is essential for guiding appropriate, individualized treatment and avoiding unnecessary surgery.