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.


  1. 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.
  2. 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.
  3. Montemurro F. Trastuzumab emtansine in HER2-positive metastatic breast cancer. Lancet Oncol. 2017;18:696-7.