TNFRSF13C and biliary tract neoplasm: Conversely, the expression of CD24 on CD25+ CD24+ CD27+ B cells is positively correlated with biliary tract cancer, confirming CD24 as a risk factor and BAFF-R (B-cell activating factor receptor) as a protective factor.BAFF-R is a surface receptor found on B cells that specifically binds to BAFF.