Escalating and de-escalating treatment in HER2-positive early breast cancer

- Adjuvant regimens with < 12 months of trastuzumab have not been found inferior to the standard duration, but the follow-up times are still short.
- Dual inhibition of HER2 improves the pCR rates in the neoadjuvant setting and is a potential strategy to improve survival in the adjuvant setting.
- Two years of adjuvant trastuzumab confers no benefit over 1 year of trastuzumab. Extending therapy with oral HER2-inhibitors shows promise.
- Adjuvant treatments of short duration exploiting dual HER2 inhibition are being explored.

The current standard adjuvant systemic treatment of early HER2-positive breast cancer consists of chemotherapy plus 12 months of trastuzumab, with or without endocrine therapy. Several trials have investigated modifications of the standard treatment that are shorter and less resource-demanding (de-escalation) or regimens that aim at dual HER2 inhibition or include longer than 12 months of HER2-targeted treatment (escalation). Seven randomized trials investigate shorter than 12 months of trastuzumab treatment duration. The shorter durations were not statistically inferior to the 1-year duration in the 3 trials with survival results available, but 2 of the trials were small and 1 had a relatively short follow-up time of the patients at the time of reporting. The pathological complete response (pCR) rates were numerically higher in all 9 randomized trials that compared chemotherapy plus dual HER2 inhibition consisting of trastuzumab plus either lapatinib, neratinib, or pertuzumab with chemotherapy plus trastuzumab as neoadjuvant treatments, but the superiority of chemotherapy plus dual HER2-inhibition over chemotherapy plus trastuzumab remains to be demonstrated in the adjuvant setting. One year of adjuvant trastuzumab was as effective as 2 years of trastuzumab in the HERA trial, and was associated with fewer side-effects. Extending 1-year adjuvant trastuzumab treatment with 1 year of neratinib improved disease-free survival in the ExteNET trial, but the patient follow-up times are still short, and no overall survival benefit was reported. Several important trials are expected to report results in the near future and may modify the current standard.