CCNB1 and esophageal squamous cell carcinoma: Besides, ubiquitin E1 inhibitor PYR‐41 rescued the expression of Cyclin B1, downregulated p21 and reduced the accumulation of G2/M phase cells in PR‐619‐treated ESCC cells, which implied that PR‐619 triggered G2/M cell cycle arrest in ESCC by regulating the expression of cyclin B1 and p21.