Mucinous Cystadenocarcinoma of the Breast with Bone Metastases: First Case Report and Literature Review

Introduction: Mucinous cystadenocarcinoma (MCA) of the breast is an extremely rare type of breast carcinoma. Since its biological characteristics, treatment options, and clinical outcomes are unclear, there is a lack of consensus regarding the optimal management of this disease. Thus, our single case report will aid our understanding of its natural history, prognostic factors, and treatment strategies. Case Presentation: We presented a 54-year-old woman with a case of advanced MCA of the breast accompanied by a huge breast mass, lymph node involvement, and distant bone metastases. We diagnosed primary breast MCA through clinical examination, imaging, and immunohistochemical assessments. Subsequently, the patient was treated with a regimen of nab-paclitaxel and bevacizumab, resulting in a significant clinical response. Progression-free survival was maintained during the 6-month follow-up period. Conclusion: We present the first report worldwide of a rare case of MCA of the breast with a large local mass and bone metastases. Our report adds to the limited literature on this rare breast cancer subtype and highlights the importance of accurate diagnosis and appropriate management of aggressive breast tumors.