PIK3CA and plasma cell myeloma: The PI3K/AKT signaling pathway regulated BCRP expression, and BCRP may protect multiple myeloma (MM) cells from the cytotoxicity of chemotherapeutic drugs by phosphatase and tensin homolog expression via a potential negative feedback loop of BCRP, and it is modulated by PTEN-mediated PI3K/AKT pathway regulation in NCI-H929 cells121.