Abstract P4-07-07: Metaplastic carcinoma of the breast has comparable prognosis to non-metaplastic triple negative breast cancer despite poor response to chemotherapy

Abstract

Abstract Introduction Metaplastic carcinoma (MC) of the breast is a rare pathologic entity accounting for <1% of all invasive breast cancers and is generally negative for hormone receptors and HER2. They often show more aggressive characteristics and are resistant to treatment. Although triple negative breast cancers (TNBCs) have good response to neoadjuvant chemotherapy (NAC) and a pathologic complete response (pCR) rate of about 40%, benefit of NAC for MC is not clear. The aim of this study was to compare the Clinicopathologic characteristics and prognosis of MC with non-MC TNBC, and assess the usefulness of NAC for MC. Methods Retrospective chart review of TNBC patients who underwent breast surgery at Seoul National University Hospital between January 2000 and December 2018 were included for analysis. Clinicopathologic features including age, TNM stage, Ki-67 and histologic grade were collected. For patients who had received NAC, tumor size on ultrasound before NAC and pathologic size of residual tumor was used to assess responsiveness to NAC. We used 3:1 propensity score matching according to age, neoadjuvant chemotherapy, pT stage, pN stage. Kaplan-Meier analysis and log-rank test were performed. Results Among 1783 TNBC patients included for analysis, 82 (4.59%) were MC and 1701 (95.34%) were non-MC. MC had a worse DFS and OS. After propensity score matching, there was no difference in survival outcomes. The 5-year disease-free survival and overall survival between MC vs. non-MC TN was 61.9% vs. 73.0% (HR 1.379, 95% CI 0.594-3.202, p-value = 0.430) and 71.4% vs. 74.6% (HR 1.007, 95% CI 0.393-2.579, p-value = 0.480), respectively. The proportion of patients who received NAC among MC and propensity matched non-MC TNBC were 21/82 (25.6%) and 63/1701 (3.7%), respectively. The pathologic complete response rate for all and propensity score matched non-MC TNBC was 76/364 (20.9%) and 11/63 (17.5%), respectively, whereas no MC patients achieved a pathologic complete response (HR 1.404 95% CI 1.213-1.624, p-value = 0.058). Conclusions MC has comparable prognosis compared to non-MC TNBC in terms of disease-free survival and overall survival, while showing lower rate of pathologic complete response after NAC. Upfront surgery may be more beneficial for MC. A prospective study with larger number of patients evaluating the role of NAC in MC is warranted. Citation Format: Changjin Lim, Jang-il Kim, Yireh Han, Jong-ho Cheun, Ji Gwang Jung, Hong Kyu Kim, Hyeong-Gon Moon, Wonshik Han, Han-Byoel Lee. Metaplastic carcinoma of the breast has comparable prognosis to non-metaplastic triple negative breast cancer despite poor response to chemotherapy [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 P4-07-07.