Abstract P1-12-03: Metaplastic carcinoma of the breast: A single-center 18-year series of 73 cases
Authors: Thériault Kassandra J , Moussa Mariem Ben , Perron Marjorie , Desbiens Christine , Poirier Brigitte , Poirier Éric , Leblanc Dominique , Morin Claudya , Lemieux Julie , Hogue Jean-Charles , Boudreau Dominique 
Published: March 2022

Abstract
Background: Metaplastic breast cancer (MeBC) is a rare subtype accounting for 0.2%-5% of all invasive breast cancer. They are characterized by an aggressive course and even a worse prognosis than triple-negative breast cancer (TNBC). The literature suggests that MeBCs are relatively chemoresistant; still, the patients often receive adjuvant or neoadjuvant chemotherapy during the course of treatment. This study aimed to examine the clinical management of MeBC, particularly the role of chemotherapy. Methods: This retrospective study included patients with MeBC (n=73) from the Centre des Maladies du Sein du CHU de Québec-Université Laval. The specimens were reviewed by two pathologists. Patient and tumor characteristics, systemic therapy (neoadjuvant and adjuvant), disease-free survival (DFS), and overall survival (OS) were recorded. Results: The median follow-up was 57.2 months. The mean tumor size was 39.5±32.1 (range, 1-200) mm. The vast majority had grade 3 (76.7%), no evidence of clinical nodal involvement (78.1%), and triple-negative (79.5%) disease. This population included one case (1.4%) of low-grade adenosquamous breast carcinoma, one (1.4%) of fibromatosis-like metaplastic carcinoma, 11 (15.1%) of spindle cell carcinoma, 13 (17.8%) of epidermoid carcinoma, 18 (24.7%) of MeBC with heterologous mesenchymal differentiation, and 29 (39.7%) of mixed MeBC. Chemotherapy was given to 53 (72.6%) patients. Thirty-seven patients (50.7%) had a lumpectomy, and 34/37 (91.9%) received adjuvant radiotherapy. Thirty-six patients (49.3%) had mastectomy and 22/36 (61.1%) received radiotherapy. The 5-year DFS was 55.6%, and the 5-year OS was 63.5 %. On univariable analyses, higher cT stage (cT3-4) was associated with poorer DFS and OS compared to cT1-2, respectively 13.4% vs. 70.7% (P&lt;0.0001) and 19.9% vs. 82.8% (P&lt;0.0001). Nodal involvement significantly influenced DFS (31.3% vs. 63.0%, P=0.011) and OS (37.5% vs. 71.6%; P=0.009). Lumpectomy was associated with a better 5-year DFS (78.4% vs. 34.0%, P&lt;0.0001) and OS (90.6% vs. 38.8%, P&lt;0.0001). The use of chemotherapy had a significant positive effect on 5-year DFS (64.2% vs. 31.9%, P=0.006; hazard ratio (HR)=0.45, 95% confidence interval (CI)=0.22-0.92, P=0.009) as well as 5-year OS (69.7% vs. 45.1%, P=0.035; HR=0.52, 95%CI=0.28-0.95 P=0.041). However, radiation therapy did not influence DFS (P=0.420) and OS (P=0.316). Nine patients received neoadjuvant chemotherapy; five had nodal involvement. One patient had a complete response (11.1%), five (55.6%) had a partial response, and three (33%) had progressive disease. The 5-year DFS and OS were lower for neoadjuvant chemotherapy compared with adjuvant chemotherapy (DFS: 27.8% vs. 71.5%, P=0.006; OS: 33.3% vs. 79.2%, P=0.001), but disease was more advanced in patients with neoadjuvant chemotherapy (cT3-4: 88.9% vs. 11.9%, P&lt;0.0001). Conclusion: MeBC represents a rare heterogeneous group of malignancies with poor prognosis. Chemotherapy was associated with improved DFS and OS. Patients for neoadjuvant chemotherapy should be carefully selected.
Citation Format: Kassandra J Thériault, Mariem Ben Moussa, Marjorie Perron, Christine Desbiens, Brigitte Poirier, Éric Poirier, Dominique Leblanc, Claudya Morin, Julie Lemieux, Jean-Charles Hogue, Dominique Boudreau. Metaplastic carcinoma of the breast: A single-center 18-year series of 73 cases [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-12-03.