• PIK3CA mutation
• breast cancer

PIK3CA mutation results in a constitutive activation of the of PI3K-AKT-mTOR pathway that is implicated in tumour progression in breast cancer (BC). Somatic PIK3CA mutations occur in 29%-45% of luminal, in 39% HER2-positive and 9% of basal-like BCs. 80% of PIK3CA mutations are located in exons 9 and 20. A recent pooled analysis of individual data showed PIK3CA mutation to be a positive prognostic factor in early stage BC. In neoadjuvant setting, pCR rates are significantly lower in PIK3CA mutant tumours treated with anti-HER2 therapy compared to wild-type group, mainly in ER-positive subgroup. PIK3CA mutation represents a negative prognostic factor and a positive predictive biomarker to PI3K inhibitors in ER-positive/HER2-negative metastatic BC. Traditionally, PIK3CA mutation can be assessed on tumour tissue drawn by invasive biopsy procedure, using Digital PCR or NGS technologies. ctDNA drawn by liquid biopsy, can be used as an alternative tool for identification of somatic mutations. Many variables as tumour burden can affect its results. Conflicting data derive from several studies evaluating the diagnostic accuracy of detecting PIK3CA mutation in ctDNA compared to tumour tissue. Furthermore, new important studies have recently been published. Therefore, the main aim of our meta-analysis is to evaluate the diagnostic accuracy of PIK3CA mutation assessment on ctDNA as compared to gold standard assessment, represented by PIK3CA mutation detected on tumour tissue.