PIK3CA and breast cancer: However, ctDNA containing PIK3CA mutations has been suggested to be a promising biomarker of cancer patients with advanced disease both for early detection of recurrence and to monitor treatment response (Board et al., 2010; Dawson et al., 2013; Higgins et al., 2012), and studies reveal a correlation of PIK3CA mutation level and tumor burden in advanced breast cancer (Garcia‐Saenz et al., 2017; Higgins et al., 2012).