As the largest family of serine proteinase inhibitors, serpins are widespread in all kingdoms, playing key roles in multitudinous physiological and phytochemical pathways, including inflammation, immunomodulation, tumorigenesis, hemolymph coagulation, PPO activation, antimicrobial activity, and cancer metastasis (Heit et al. 2013; Meekins et al. 2017; Schemczssen-Graeff et al. 2021; Zhang et al. 2021a). Here, PPOX is linked to cancer.