Review of treatment strategies for HER2 positive breast cancer and their implementation in a major Swiss hospital
Geissler F.1, Vetter M.2,3,4, Schoetzau A.1, Montavon C.1,2, Kurzeder C.1,2,5, Heinzelmann V.1,2, Schwab F.D.1,5,6
1Department of Gynecology and Gynecological Oncology, University Women`s Hospital of Basel, University of Basel, Basel, Schweiz, 2Gynecological Cancer Center, University Hospital Basel, Basel, Schweiz, 3Breast Cancer Center, University Hospital Basel, Basel, Schweiz, 4Department of Medical Oncology, University Hospital Basel, Basel, Schweiz, 5Breast cancer Center, University Hospital Basel, Basel, Schweiz, 6Gynaecological Cancer Center, University Hospital Basel, Basel, Schweiz

Introduction: In Switzerland, breast cancer (BC) is diagnosed in around 6,000 women per year. The human epidermal growth factor receptor 2 (HER2) is overexpressed in 15-20%. This study aims to overview the implementation of treatment strategies in the clinical routine of a Swiss Cancer Center.
Methods: A retrospective data analysis of 158 patients with newly diagnosed HER2+BC between 2008-2018 at the University Hospital of Basel was performed. All statistical evaluations were done using the software R.
Results: The cohort contains 70,3% (n=111/158) patients with early BC (Stage I-IIB), 17,1% (n=27/158) with locally advanced BC (Stage IIIA-IIIC) and 12,6% (n= 20/158) with Stage IV disease at first diagnosis. In our cohort 89.9% (n=142/158) were treated with HER2-targeted therapy (HTT). Surgery as initial treatment in small, node-negative tumors, was performed in 3.16% (n=5/158). Overall 28.5% (n=45/158) received neoadjuvant treatment (NAT) and 68.9% (n=31/45) a HER2 dual blockade plus chemotherapy. A pathological complete response (pCR) was achieved in 57.8% (n=26/45) with NAT and 70.8% (n=17/24) of node-positive patients were node-negative after NAT. Palliative treatment (PT) with HTT was conducted in 95% (n=19/20).
Conclusion: Trastuzumab was approved for PT of HER2+BC in 1999 and for adjuvant treatment in 2006. Dual HER2 blockade with Pertuzumab and Trastuzumab was authorized in 2013 for metastatic BC and expanded to NAT for locally advanced HER2+BC in 2016. New HTT such as TDM1 were introduced for PT and recently for patients with non-pCR after NAT. Awareness of current guidelines helps improving patient's individual care and balance under-/overtreatment.