COMPARISON OF TREATMENT RESPONSE IN SUBSEQUENT LINES TO T-DM1 IN PATIENTS WITH HER2 POSITIVE METASTATIC BREAST CANCER

Background: Breast cancer has a strong epidemiological impact. Approximately 20% are HER-2 positive. In the metastatic scenario, first-line treatment was consolidated with the CLEOPATRA study and second-line treatment with trastuzumab-entamsine (T-DM1) with the EMILIA study. But the third line is still challenging. Objectives: To compare the Overall Survival (OS) of patients undergoing T-DM1 and subsequent lines, in the setting of HER2 positive metastatic breast cancer. Secondarily compare Progression Free Survival (PFS), Time to Treatment Failure (TTF), clinical response and serious adverse events. Methods: Retrospective, single-center study. It included 67 patients with HER2-positive, metastatic breast cancer exposed to T-DM1 between August 2013 to December 2021. Of the total of 67 patients, 38 received subsequent lines. Median follow-up of 34 months. Descriptive statistics was used to assess the characteristics of the population. Categorical variables were described using frequencies and percentages. Numerical variables were described by measures of central tendency and central dispersion. Associations between categorical variables were assessed using chi-square or Fisher tests, when appropriate. The time-to-event variables were analyzed using Kaplan Meier curves and the comparison between them was performed using the Log Rank test and Cox regression. Univariate and multivariate analyzes by Cox regression were performed to define predictive factors associated with PFS, TTF and OS. Results: Median T-DM1 PFS was 15 months. The main features related to PFS were: absence of visceral metastasis, HER-2+++ and ECOG < 2. Median OS of T-DM1 was 47 months. The main factors related to OS were ECOG <2, HER2 +++, absence of serious adverse events and use of pertuzumab. Treatments subsequent to T-DM1 were divided into 3 groups: Group 1 = capecitabine + lapatinib (21 patients); Group 2 = deruxtecan (5 patients) and Group 3 = other chemotherapy agents (12 patients). The PFS in Group 2 had an average of 24 months, in Group 1 an average of 14 months and in Group 3 there was an average of 10 months. In terms of Overall Survival, there were no deaths in group 2, in Group 1 it ranged from 2 to 68 months and in Group 3 it ranged from 2 to 32 months. Conclusion: Deruxtecan had numerically superior PFS . Capecitabine plus lapatinib was numerically superior in PFS compared to other treatments with the exception of Duruxtecan.