Pitfalls and mass-forming mimics of pancreatic cancer

The diagnostic pathway of pancreatic lesions has changed since endoscopic ultrasound-guided biopsies were introduced. The tissue diagnosis of pancreatic ductal adenocarcinoma (PDAC) used to be made by cytology or surgical specimens, while pancreatic biopsies currently contribute to a pretreatment diagnosis in >80 % of cases. Pathologists need to assess subtle changes in biopsy specimens, in order to avoid over- and under-diagnosis of PDAC. The lack of stromal reaction does not exclude the possibility of PDAC, while abnormal distribution of the ducts and a mild but sufficient degree of nuclear atypia are diagnostic clues for well differentiated PDAC. It is also important to be aware of distinct types of pancreatitis that potentially presents with a tumour. IgG4-related autoimmune pancreatitis (type 1 AIP) is widely recognised as a mimic of PDAC. Other forms of mass-forming pancreatitis include type 2 AIP (IgG4-unrelated), follicular pancreatitis, groove pancreatitis and acute interstitial pancreatitis. Most of those conditions lack serological diagnostic markers; therefore, the histology plays a central role in the diagnosis.