Background: The majority of breast cancer patients in Mexico are treated through the public health system and >80% receive adjuvant chemotherapy. The aim of this prospective study was to characterize the impact of the Oncotype DX assay on adjuvant therapy decision making and the confidence in those decisions amongst public sector physicians in Mexico. Methods: Ninety-eight consecutive patients with ERþ, HER2À, stage I-IIIa, N0/N1-3 node-positive breast cancer from the Instituto Nacional de Cancerología were eligible for the study. The primary endpoint was the overall change in treatment recommendations after receiving the assay results. Results: Of 96 patients, 48% received a chemohormonal therapy recommendation prior to testing. Following receipt of results, treatment decisions changed for 31/96 (32%) patients, including 17/62 (27%) node-negative patients and 14/34 (41%) node-positive patients. The proportion of patients with a chemotherapy-based recommendation decreased from 48% pre-to 34% post-assay (P ¼ 0.024). 92% of physicians agreed that they were more confident in their treatment recommendation after ordering the assay. Conclusions: These results suggest that use of the 21-gene assay in the Mexican public health system has a meaningful impact on adjuvant treatment recommendations that may reduce the overall use of chemotherapy.

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e12545 Background: Breast cancer in pregnancy is that diagnosed during pregnancy or in the first year after birth (1), is the most frequent malignant neoplasms during pregnancy, (2,3); however, only 0.2% to 2.9% of all breast cancers occur during pregnancy(4), the incidence of breast cancer during pregnancy (BCDP) has increased the last few decades probably because of the delayed childbearing and the rise of maternal age (5,6). Because of the rarity of cases and the impracticability of conducting randomized controlled studies in this setting, several studies are retrospective, whilst some studies suggest outcomes for women are similar to non-pregnant patients with breast cancer(8–11), others (12–17) have demonstrated that pregnancy in itself is an adverse prognostic factor for survival. To contribute with the existing literature, we aimed to perform a cohort to analyze if there is a difference prognosis of patients with BCDP who started treatment during pregnancy or waited for delivery. Methods: We analyzed the baseline characteristics distribution in the BCP using the chi-square test and the Fisher’s exact test for categorical variables. We considered a statistically significant association when p value was < 0.05. DFS and OS analyses were conducted using the Kaplan–Meier method, and the log-rank test was used to determine if there were any differences in the survival curves by the variables of interest. We performed the statistical analysis using the SPSS 25.0 software for Windows (SPSS Inc., Chicago, IL, USA). Results: Among 8037 breast cancer patients enrolled in the database at Instituto Nacional de Cancerología, Mexico (INCan), within the social security program named “Seguro Popular”, between January 2007 and June 2018, we identified and included 61 women, median maternal age at diagnosis in our BCP group was 35 years (range 21-47), triple negative and her2 comprised 50.8% and 49.2% of BCP is comprised by luminal tumors. Conclusions: We strongly believe that the treatment of breast cancer during pregnancy should be started as soon as possible, since we have seen that its delay in childbirth translates into worse disease-free and overall survival. [Table: see text][Table: see text]

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