CDKN1B and in situ carcinoma: The p27Kip1-nuclear positive ratio in CIS was the lowest during IPMN progression, and the p27Kip1-nuclear positive ratio (13.1%) in malignant lesions (CIS and invasive carcinoma) was significantly lower than that (22.4%) in normal and non-malignant lesions (normal duct, adenoma, and borderline atypia) (p = 0.0158).