A 14-year retrospective of HER2 + metastatic breast cancer treatment at one comprehensive cancer center: Impact of the trastuzumab/pertuzumab and trastuzumab-emtansine sequence versus trastuzumab on overall survival.

Introduction: Monoclonal antibodies represent a significant improvement in the treatment of the HER2 + metastatic cancer, which is associated with a worse prognosis. The objective of this study was to compare overall survival (OS) data in patients treated with trastuzumab + pertuzumab followed by trastuzumab-emtansine (T-DM1) in the second line of metastatic treatment (Arm A) versus patients treated with trastuzumab alone (Arm B). Progression-free survival (PFS) in first-line metastatic patients was also compared in both arms. Methods: This single-center retrospective study included patients from February 2008 to August 2022. OS and PFS of both arms were described and estimated using the Kaplan-Meier method. Data were extracted from electronic medical records and CHIMIO prescribing software. Results: The total duration of metastatic treatment of the 82 patients was significantly longer in the arm A (43.2 ± 28 months vs 33.6 ± 28.9 months), as was the median time to death (59 vs 52 months). The OS data showed a significant reduction in the risk of death in the arm A (Hazard Ratio = 0.59; 95% Confidence Interval [0.37-0.94]; p = 0.02). No difference was shown for PFS. Conclusion: The trastuzumab/pertuzumab/T-DM1 combination showed a significant improvement in OS. Our results are in line with the CLEOPATRA and EMILIA studies, but long-term responders in the arm A may have impacted our results. The absence of difference in term of PFS in first metastatic line may be explained by a selection bias, as patients in the arm A potentially have more aggressive forms.