SKP2 has been recognized as an oncogenic protein, which promotes the cell cycle progression by facilitating the degradation of p21 and p27.34 Significant accumulation of p21 was observed in CYH33-sensitive ESCC cells, which indicated the crucial role of p21 in inducing G1 phase arrest upon PI3K inhibition. This evidence concerns the gene SKP2 and esophageal squamous cell carcinoma.