Retrospective analysis of HER2 therapy interruption in patients responding to the treatment in metastatic HER2+ breast cancer

INTRODUCTION: Human epidermal growth factor receptor 2 (HER2)-targeted-therapy regimens can lead to prolonged tumour responses in metastatic HER2+ breast cancer. Clinical trials have concerned use of HER2-targeted agents until disease progression, but it is unknown whether the therapy can be interrupted in cases of a good response. METHODS: Single institute, retrospective collection of data on patients with HER2+ metastatic breast cancer (n=68) was carried out through a pharmacy search for patients who had received trastuzumab in 2006–2014. Clinical and pathological factors, treatment history and survival data were collected from patient records. RESULTS: Median survival in metastatic disease (all patients) was 32 months and survival times were dramatically different in patients with and without trastuzumab as adjuvant or primary metastatic disease (median 16, 77 and 35 months, respectively; p=0.0004). More importantly, HER2 therapy was intentionally interrupted in 21 responding patients, and these patients experienced long HER2-therapy-free intervals (median 51 months), with excellent long-term survival. A lack of previous adjuvant trastuzumab was the only statistically significant factor predictive of HER2 therapy interruption. CONCLUSIONS: These results from our retrospective study show that HER2 therapy interruption in patients with metastatic HER2+ breast cancer, who have responded to the therapy, is associated with low risk of rapid disease progression. Study suggests that therapy interruption in cases of response and reinitiation in progression is feasible.