Intraductal oncocytic papillary neoplasm (IOPN): two case reports and review of the literature.

Background: Intraductal oncocytic papillary neoplasms (IOPNs) place at the oncocytic extreme of the intraductal pancreatic neoplasm spectrum and display typical morphological features. Their identification in 1996 by Adsay has been followed by a growing number of cases, paving the way for a deeper understanding of this underestimated entity. Contrarily to intraductal papillary mucinous neoplasms (IPMNs), most IOPNs run an indolent course and surgery is usually curative. Pancreatic IOPNs tend to develop from the main pancreatic duct (MPD) and their diagnosis is either incidental or subsequent to mass-related symptoms. Up to 30% of cases show concomitant areas of minimal stromal invasion and loco-regional or systemic spread are confined to a minority of cases. Biological hallmarks of IOPNs are being identified, including recurrent kinase gene rearrangements. Morphological and biological traits of IOPNs seem to overlap with those of other malignancies. A deeper understanding of these entities is needed in order to shed light upon the nature of pancreato-biliary oncocytic neoplasms. This case report describes two patients with a diagnosis of IOPN-one of them accounting for the largest IOPN ever described-and provides a brief review of recent discoveries on the subject.

Case Description: We describe two cases of IOPN occurring in adult male patients, respectively in their 60s and 70s. Both patients had unremarkable clinical history. In case 1 the diagnosis was coincidental to a right renal colic; case 2 complained a right lumbar pain radiating to the homolateral groin. In both cases imaging analyses revealed a voluminous pancreatic mass, posing the indication to laparoscopic pancreatectomy. Gross and histological features were consistent with the diagnosis of IOPN. Surgical margin were free from disease and the patient did not undergo further treatment. After a 10- and 7-month follow-up respectively, patients did not experience relapse.

Conclusions: Recent immunohistochemical (IHC) and molecular data reveal unique characteristics of IOPNs, highlighting the substantial differences from IPMNs. Further research is needed in order to identify novel prognostic and predictive markers applicable to oncocytic neoplasms of the pancreato-biliary tract.