CCR4 and pancreatic ductal adenocarcinoma: Enhanced infiltration of CCR4+ Treg cells has been associated with unfavorable prognoses in different cancer types, including pancreatic ductal adenocarcinoma, prostate cancer, and colorectal cancer (Grage-Griebenow et al., 2014; Wang et al., 2019b; Watanabe et al., 2019).