PIGR and rectal cancer: For example, the pIgR expression level in the mouse small intestine is higher after weaning than before [6], while in rats, pIgR expression in small intestine appears only after weaning [7]; the pIgR expression level is significantly higher in the rodent liver than in the respiratory tract [3]; and in diseases such as human lung cancer and rectal cancer, pIgR expression levels are decreased, or even absent [8, 9].