CTA: What other studies are ongoing in support of this treatment rationale?
Dr Montemurro: I am not aware of studies evaluating a different timing of T-DM1 and, honestly, it could be difficult to conduct one that would randomize patients to early or delayed initiation of T-DM1 for metastatic disease.
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One possibility would be testing a biomarker-guided approach, where a biological feature that predicts for increased or decreased activity of a certain anti-HER2 treatment could guide treatment choices. I would really like to see such a study.
CTA: What proportion of patients is expected to benefit with this treatment?
Dr Montemurro: The proportion of patients showing tumor regression during T-DM1 treatment was about 40% in the EMILIA trial, and slightly less (30%) in the TH3RESA trial, once again arguing in favor of an earlier use of T-DM1 in patients with HER2-positive metastatic breast cancer.
In both trials, tumor regression was significantly more frequent with T-DM1 than in control arms, with an incremental difference of +10% in the EMILIA and +23% in the TH3RESA trial.
CTA: What should clinicians understand about this treatment?
Dr Montemurro: T-DM1 is an important addition to the therapeutic armamentarium of the treatment of HER2-positive metastatic breast cancer. Its role is now consolidated in patients with trastuzumab resistant HER2-positive breast cancer and it can be active and efficacious also in patients with extensively treated disease.
Furthermore, being the first of its class in this patient setting, T-DM1 has paved the way for other antibody-drug conjugates that will become available in the future and offer new hopes for patients with this type of breast cancer.
References
- Diéras V, Miles D, Verma S, et al. Trastuzumab emtansine versus capecitabine plus lapatinib in patients with previously treated HER2-positive advanced breast cancer (EMILIA): a descriptive analysis of final overall survival results from a randomised, open-label, phase 3 trial. Lancet Oncol. 2017;18:732-42.
- Krop IE, Kim SB, Martin AG, et al. Trastuzumab emtansine versus treatment of physician’s choice in patients with previously treated HER2-positive metastatic breast cancer (TH3RESA): final overall survival results from a randomised open-label phase 3 trial. Lancet Oncol. 2017;18:743-54.
- Montemurro F. Trastuzumab emtansine in HER2-positive metastatic breast cancer. Lancet Oncol. 2017;18:696-7.
