Pancreatic ductal adenocarcinoma (PDAC) is one of the leading causes of cancer death. Although the treatment modalities are improving, the prognosis of PDAC continues to be poor. Therefore, early detection of PDAC or its precursor lesions may be the best way to improve patient survival. PDACs have several different precursor lesions, including pancreatic intraepithelial neoplasias (PanINs), intraductal papillary mucinous neoplasms (IPMNs), intraductal tubulopapillary neoplasms (ITPNs), intraductal oncocytic papillary neoplasms (IOPNs), and mucinous cystic neoplasms (MCNs). PanINs cannot be identified using imaging modalities, while the other lesions are radiologically detectable. These precursor lesions are categorized based on structural and cytological atypia as low-grade and high-grade lesions. We discuss recent updates regarding histopathological and molecular pathological overviews of PDAC precursor lesions. Better understanding of such lesions may contribute to earlier detection of PDAC or its precursor lesions and improve PDAC patient survival.

Aims Histology‐based tumour microenvironment (TME) scores are useful in predicting the prognosis of gastrointestinal cancer. However, their prognostic roles in distal bile duct cancer (DBDC) have not been previously studied. This study aimed to evaluate the prognostic significance of the TME scores using the Klintrup–Mäkinen (KM) grade, tumour stroma percentage (TSP) and the Glasgow microenvironment score (GMS) in resected DBDC. Methods and results Eighty‐one patients with DBDC who underwent curative resection were enrolled. DBDC was graded according to KM grade, TSP and GMS. A high KM grade was found in 19 patients (24%) and a high TSP was found in 47 patients (58%). A high TSP was significantly correlated with a low KM grade (P < 0.001). The distribution of the GMS, which was developed by combining the KM grade and TSP, was as follows: 0 (n = 19, 24%), 1 (n = 19, 24%) and 2 (n = 43, 52%). A low KM grade, high TSP and high GMS were significantly associated with short overall survival (OS) (P < 0.001) and relapse‐free survival (RFS) (P < 0.001). Furthermore, multivariate analysis showed that a low KM grade [hazard ratio (HR) = 3.826; confidence interval (CI) = 1.650–8.869; P = 0.014], high TSP (HR = 2.193; CI = 1.173–4.100, P = 0.002) and high GMS (HR = 7.148; CI = 2.811–18.173) were independent prognostic factors for short RFS; a low KM grade (HR = 4.324; CI = 1.594–11.733) and high GMS (HR = 6.332; CI = 2.743–14.594) were independent prognostic factors for short OS. Conclusion Histology‐based TME scores, including the KM grade, TSP and GMS, are useful for predicting the survival of patients with resected DBDC.