Outcomes and clinicopathological characteristics of patients with metaplastic breast cancer at the National Cancer Institute Mexico between 2016-2020.

e12747 Background: Metaplastic breast cancer is a rare histological subtype (< 1%) with dismissal prognosis and few studies regarding patient outcomes and characteristics. Information in Latin America is scarce, therefore our primary objective was to determine Survival Outcomes and Clinicopathological characteristics in a Tertiary Cancer Center in Mexico. Methods: This was a prospective cohort of metaplastic breast cancer patients between 2016-2020 at the National Cancer Institute in Mexico City whether they went to primary systemic therapy or not. For descriptive statistics we used frequencies and proportions. A Kaplan-Meier analysis was performed for Overall Survival, Progression-Free Survival and Recurrence-Free Survival outcomes. Results: The most relevant clinicopathological characteristics are presented in Table 1. Median tumor size was 4.3cm (1-30); 48% underwent neoadjuvant chemotherapy of which 8% (1) had ypT0, 58% (7) ypN0. In upfront surgery patients, 63% (7) were pT1-pT2, and 55% (6) were pN1-pN2. 67% (28) had mastectomy and 48% (13) had axillary dissection. Median follow-up was 67 months (51-82), there were 8 deaths (median survival not reached), 2 recurrences (median recurrence 28 months) and 1 progression. Conclusions: Metaplastic breast cancer in this population consisted of high grade tumors, advanced stages, predominantly triple negative breast cancers and no HER2+ subtypes. 70% of patients had a ductal component, with 52% of nodal disease at presentation. This is an interesting finding since nodal disease in these tumors is not usually reported. Median survival was not reached with a follow-up of more than 5 years, which gives insight on the prognosis of a rare breast cancer subtype in the largest cohort reported in Mexico so far. Clinicopathological characteristics of patients with metaplastic breast cancer. % (n) Age 52 (39-79)* Clinical StageIIIIIIIV 12 (3)19 (5)54 (14)15 (4) T Stage1234 19 (5)26 (7)18 (5)37 (10) Nodal StagecN 0cN 1cN 2cN 3 48 (13)19 (5)26 (7)7 (2) Subtype HR+HER2-HR-HER2-HER2+ 33 (9)67 (18)0 (0) GradeIIIIIIN/A 4 (1)11 (3)56 (15)30 (8) Ductal componentYesNoN/A 70 (19)26 (7)4 (1) Neoadjuvant ChemotherapyYesNoN/A 48 (13)48 (13)4 (1) Adjuvant ChemotherapyYesNoN/A 70 (19)26 (7)4 (1) *Median (range).