Clinical analysis of metaplastic breast carcinoma with distant metastases: A multi‑centre experience

Metaplastic breast cancer (BC-Mp), which includes a range of epithelial and mixed epithelial-mesenchymal tumours, are rare malignancies with an unfavourable prognosis. The limited literature on BC-Mp focuses mainly on retrospective data for radically treated patients. Notably absent are studies dedicated to the palliative treatment of BC-Mp with distant metastases. The present retrospective study investigated treatment modalities and prognosis in a multi-centre cohort of 31 female participants diagnosed with distant metastatic BC-Mp, including 7 patients with de novo metastatic disease. The median age of the patients was 61 years (range, 33-87 years), with 38.7% presenting local lymph node involvement. Lungs were the most common site for the metastatic disease (61.3%). Median Ki-67 index was 50% (range, 35-70%), and 80.7% of cases were classified as grade 3. Human epidermal growth factor receptor 2 (HER2)⁺ and estrogen receptor⁺ were detected in 12.9 and 6.5% of cases, respectively. A total of 62.4% of patients received first-line palliative systemic treatment. The 1- and 2-year overall survival (OS) were 38.5 and 19.2%, respectively. Receiving ≥1 line of palliative treatment was significantly associated with improved OS (P<0.001). Factors such as age, Ki-67 index, HER2 or hormonal status, presence of specific epithelial or mesenchymal components, location of metastases or chemotherapy regimen type did not influence OS. The present study provided insights into the clinicopathological profile, systemic treatment experience, prognostic factors and OS data of BC-Mp with distant metastases, emphasizing the imperative for clinical trials in this population.