Impact of progression sites and line of therapy on survival outcomes in patients with HER-2 positive metastatic breast cancer treated with T-DM1.

Objective: Ado-trastuzumab emtansine (T-DM1) is a key treatment for HER2-positive metastatic breast cancer (HER2+ MBC), yet the influence of progression sites and therapy lines on outcomes remains unclear.To assess the relationship between progression sites and the line of T-DM1 therapy with survival outcomes in HER2+ MBC.

Methods: We retrospectively analyzed 123 patients with HER2+ MBC treated with T-DM1. Data on metastatic progression sites (brain, liver, bone, lung, lymph nodes), line of T-DM1 therapy (2^nd-line vs ≥3^rd-line), and death status were examined. Due to limited survival time data, mortality was used as the primary outcome. Death rates were compared across subgroups using descriptive statistics.

Results: Brain and lung progression were associated with the highest mortality rates (76.7% and 73.1%, respectively). Liver and bone progression also showed elevated death rates (70.0% and 64.3%). Notably, more patients who used T-DM1 as the second-line therapy had a higher mortality rate at 66.7% compared to those treated with it in the third line or after (45.1%).

Conclusion: Progression to brain and lung during T-DM1 treatment correlates with higher mortality. Early-line use of T-DM1 may be linked with worse outcomes, possibly due to more aggressive disease biology. The obtained data could inform the decision-making process when treating patients with HER2+ MBC and predict their prognosis.