Predictors of successful neoadjuvant treatment in HER2‑positive breast cancer

The prognosis of local or locally advanced human epidermal growth factor receptor 2 (HER2)-positive breast cancer after a complete response from neoadjuvant systemic treatment (NAT) is excellent. However, some of the patients succumb to their disease, so novel predictive factors to identify these patients at risk are needed. Retrospective data from 119 patients treated at the Helsinki University Hospital Comprehensive Cancer Centre (Helsinki, Finland) were collected. All patients had in situ hybridization-confirmed HER2-positive breast cancer and underwent NAT with a curative intention. The primary tumours were relatively large, most patients had cytologically confirmed lymph node metastases and the treatments used were current regimens. A total of 63 (52.1%) patients had a pathological complete response (pCR) to neoadjuvant therapy. Achieving pCR predicted longer disease-free survival (DFS; P=0.0083) but not overall survival (P=0.061). The patients with a pCR had an estimated DFS rate of 96.8% at 5 years, compared with only 59.7% of the patients with non-pCR. Radiological complete response (CR) was associated with pCR (P=0.00033), although imaging yielded 30.4% false-negative and 36.9% false-positive results. The association between the radiological CR and pCR was more obvious in oestrogen receptor-negative tumours. Moderate (compared with strong) immunohistochemical HER2 expression predicted a lower chance of pCR (P=0.0078) and worse breast cancer-specific survival (P=0.0015). In conclusion, pCR after NAT served as an important prognostic factor in women with high-risk HER2-positive breast cancer. The patients with only moderate immunohistochemical HER2 expression had a lower chance of reaching a pCR, as well as a shorter breast cancer-specific survival.