Matrix-producing Carcinoma as an Aggressive Triple-negative Breast Cancer: Clinicopathological Features and Response to Neoadjuvant Chemotherapy.

Background: Breast matrix-producing carcinomas (MPCs) are rare, and usually triple-negative (TNBC; i.e. oestrogen receptor-, progesterone receptor-, and human epidermal growth factor receptor 2-negative). This study evaluated the clinical features, immunohistochemical profiles, and pathological response to neoadjuvant chemotherapy (NAC) of patients with MPCs.

Patients And Methods: Five MPCs were identified among 247 patients with TNBC receiving anthracycline- and taxane-based NAC. Pathological response was assessed using surgical specimens.

Results: All tumours were histological grade 3 according to pre-treatment core biopsies. Mean Ki-67 and p53 positivity were 65% and 90%, respectively. All tumours were TNBC, and epidermal growth factor receptor-, cytokeratin 5/6-, and vimentin-positive. Grade 3 (pathological complete response) was achieved in 0% (0/5) and 32% (77/242) of those with MPCs and with TNBCs of no specific histological type, respectively, and grade 1a (poor response) in 80% (4/5) and 13% (31/242), respectively.

Conclusion: MPCs are basal-type TNBCs expressing epithelial-mesenchymal transition markers, with a poor response to standard NAC. Further studies are needed to improve the treatment of this rare but aggressive tumour.