PIK3CA and breast cancer: Furthermore, an early study found a higher level of PD-L1 expression in breast tumor specimens with PIK3CA mutation or PTEN loss than in those with wild-type versions of these genes, and the pan-PI3K inhibitor wortmannin could attenuate PD-L1-elicited immunosuppression by blocking S6K1-mediated transcription of PD-L1 in BC cells with activated PI3K [111].