Prognostic factors on her2-positive metastatic breast cancer patients treated with trastuzumab emtansine – real-world study

Sousa M.J.1, Magalhães J. C.1, Basto R.1, Garcia A. R.1, Pazos I.1, Sousa G.1 1Oncology Institute of Coimbra, Portugal

Metastatic breast cancer remains virtually an incurable disease, however, improved overall survival (OS) has been observed recently for certain subtypes, particularly on HER2-positive disease. Trastuzumab emtansine (T-DM1) is the standard second-line treatment for HER2-positive metastatic breast cancer (HER2+ MBC) patients who have progressed to taxanes and trastuzumab. This study aimed to explore prognostic factors for long-term survival from T-DM1 treatment.

We performed a single-centre retrospective analysis of HER2+ MBC patients treated with T-DM1 between April 2016 and January 2021. Stage, hormone-receptor positivity, number of metastatic sites, visceral metastases, brain metastases and previous treatment with dual anti-HER2 blockade were investigated as prognostic factors. Statistical analysis was performed using univariate and multivariate analysis from SPSS 27.0 software.

We identified 35 female patients diagnosed with HER2+ MBC since 1994. At the time of T-DM1 treatment, the median age was 57 years (range 33-81); 94% ECOG PS 0-1; 60% had hormone-receptor/HER2 positive, 9% with stage I, 34% stage II, 31% stage III and 26% stage IV; 54% were grade 2; 60% had ≤ 2 metastatic sites; 74% had visceral metastases; 23% had brain metastases and 54% were previously treated with dual anti-HER2 blockade. Median follow-up duration was 10.2 months. Median OS (mOS) was 25.7 months (95% 12.0-39.5). Three or more metastatic sites [mOS 10.2 months (95% CI 3.2-17.1, p <0.05)] and the presence of brain metastases [mOS 5.5 months (95% CI 3.0-8.0, p<0.001) were associated with significantly shorter mOS.

Even though we have a small study sample, 2 or less metastases sites and the absence of brain metastases seem to be indicators of a good prognosis in HER2+ MBC treated with T-DM1.