Metaplastic breast cancer: a clinicopathological analysis of nine cases highlighting diagnostic challenges and aggressive behavior.

Introduction: Metaplastic breast cancer (MBC) is a rare and highly heterogeneous subtype of breast cancer associated with limited treatment options and a poor prognosis. We aimed to characterize the clinical features, pathological findings, treatment patterns, and outcomes of patients with MBC. Methods: This single-center retrospective analysis included nine patients diagnosed with MBC at Hanzhong Central Hospital between January 2016 and July 2025. Clinical data, pathological features, treatment regimens, and follow-up outcomes were comprehensively reviewed. Results: Patient ages ranged from 26 to 76 years, with tumor diameters ranging from 1.5 cm to 7.0 cm, presenting as irregular hypoechoic masses on ultrasound. Immunohistochemical analysis revealed that the majority of cases (7/9, 77.8%) were triple-negative; one case (11.1%) was ER-low positive, and one case (11.1%) converted to HER2-positive following neoadjuvant therapy. All patients underwent mastectomy, with some undergoing additional lymph node dissection and radiotherapy. The most common metastatic sites were the liver and brain. At a median follow-up of 24 months (range: 15.7-28.4 months), five patients (55.6%) died from distant metastasis. Discussion: Preoperative diagnosis of MBC remains challenging and relies heavily on postoperative pathological examination. In this single-center series of nine patients, we observed aggressive clinical behavior characterized by a high rate of distant metastasis (liver and brain) and a short-term mortality of 55.6% (five of nine) at a median follow-up of 24 months. However, three patients remained disease-free, and one was alive with metastatic disease at the last follow-up, reflecting the heterogeneous clinical outcomes of this disease. The small sample size and the absence of molecular profiling preclude definitive conclusions regarding optimal treatment sequencing. Our findings underscore the diagnostic complexity, pathological heterogeneity, and urgent need for multicenter collaborative studies with integrated genomic characterization to guide future therapeutic strategies. The molecular data on PIK3CA mutation frequencies and targeted therapeutic approaches discussed in the context of the literature are derived from published studies and were not investigated in our cohort.