INSTITUTIONAL ANALYSIS OF METAPLASTIC BREAST CANCER

Objectives: Metaplastic breast cancer (MBC) is a rare histologic subtype that is characterized by squamous differentiation of the epithelium and/or mesenchymal elements that may include osseous, chondroid, or spindle cell features. MBC is typically included as a triple negative breast cancer (TNBC). However, effective strategies to treat TNBC, like neoadjuvant chemotherapy, might be ineffective against MBC given the differing tumor biology. We performed this study to achieve a better understanding of our institution’s experience with MBC including response to neoadjuvant chemotherapy compared to other forms of TNBC.

Methods: Using our tumor registry we identified all patients diagnosed with MBC from January 2012 - July 1, 2022. The diagnosis was confirmed by our institution’s pathology department in all cases. For comparison, a control group of all TNBC patients diagnosed during the 2020 calendar year were identified with MBC patients excluded. Patients who did not complete care at our institution were excluded. Demographic data, tumor and nodal characteristics, management strategies employed, response to systemic chemotherapy, and treatment outcomes were recorded.and compared between TNBC and MBC groups. Fisher’s exact test was used for categorical variables. Wilcoxon non-parametric, two-sided test was utilized for continuous variables.

Results: A total of 22 patients were included in the MBC group and 42 in the TNBC group. The pertinent clinicopathologic characteristics are included in the table below.

None of the patients in the TNBC group have recurred at short interval follow up, while 5 (22.7%) have recurred in the MBC group at a median follow-up of 5 years.

Conclusion: In our limited patient volume experience, MBC is unlike the more common types of triple negative breast cancer. Treatment strategies for MBC that include neoadjuvant chemotherapy, require more in depth study to determine efficacy. This rare tumor would benefit from a multi-institutional study of presentation, treatment, and outcomes in order to ensure the use of the most effective available therapies.