PIK3CA in HER2+ BC and pCR Trial

Women with breast cancer (BC) overexpressing HER2 have more aggressive tumors and, without administration of anti-HER2agents, a shorter disease-free survival (DFS) and overall survival (OS) compared to patients with HER2-negative subtypes. Since the introduction of trastuzumab, the course of HER2-positive BC has notably improved in both metastatic and early settings. Indeed, anti-HER2 treatment has influenced the response to neoadjuvant (NAD). Women with breast cancer (BC) overexpressing HER2 have more aggressive tumors and, without administration of anti-HER2agents, a shorter disease-free survival (DFS) and overall survival (OS) compared to patients with HER2-negative subtypes. Since the introduction of trastuzumab, the course of HER2-positive BC has notably improved in both metastatic and early settings. Indeed, anti-HER2 treatment has influenced the response to neoadjuvant (NAD) therapy in HER2-positive BC by increasing the pCR rate. However, primary and acquired resistance to trastuzumab-containing regimens remains one of the major issues in clinical practice. Selecting patients that will benefit from anti-HER2 treatment is therefore essential. Overexpression of HER2 is identified in ∼20% of early-stage invasive BC and induces the downstream activation of the PI3K/AKT/mTOR pathway that plays a crucial role in developing resistance to trastuzumab: PIK3CA mutation and PTEN protein loss cause an hyperactivation of the pathway, whereas PIK3CA wild-type and retained or increased PTEN expression lead to a lower activation. PIK3CA mutations are predominantly found in hotspots located in the helical and kinase domains (exons 9 and 20), resulting in activation of the kinase. Another potential mechanism of resistance to trastuzumab is the estrogen receptor (ER) in those tumors that express both ER and HER2. To date, resistance biomarkers are lacking: despite the fact that data on PIK3CA mutations demonstrate significantly lower pCR rates, this has not led to an inclusion of the marker into routine diagnostics. PIK3CA can be investigated together with HER2 in pre-NAD tissue samples, in order to evaluate the correlation with response to NAD chemotherapy. That is an optimal setting to understand if PI3K could be considered a biomarker for HER2 therapy-resistant tumors and to select patients with poorer prognosis. This study investigates the association of pCR with PIK3CA mutations and ER status and their prognostic value in HER2-positive BC treated with anti-HER2 therapy in addition to NAD chemotherapy. Response to NAD therapy will be determined as pCR, defined as no invasive residuals in breast tissue and lymph nodes (ypT0/is, ypN0). Disease-free survival (DFS) will be defined as time in months from randomization to (local or distant) disease recurrence, secondary malignancy or death due to any cause. Overall survival (OS) was defined as time in months from randomization to death due to any cause.