PIK3CD and breast cancer: In addition, our findings of co-treatment with the dual PI3K/mTOR inhibitor PQR309 and gemcitabine resulting in p-STAT3 blockage are in line with previously shown evidence of PI3K/mTOR signaling pathway-mediated STAT3 activation [67, 68], and STAT3 inhibitors sensitizing mouse PIK3CA-mutant breast cancer to PI3K inhibitors [69].