PIK3CA and oral cavity squamous cell carcinoma: Notably, the therapeutic efficacy of palbociclib plus selective PI3K pathway inhibitors was also investigated preclinically or in clinical trials among other solid tumors (e.g., breast cancer [58, 59], oral squamous cell carcinoma [60], and hepatocellular carcinomas [61]), supporting our conclusion that PI3K inhibitors were promising synergistic agents for palbociclib-based treatment.