Is intraductal papillary mucinous neoplasm associated with extrapancreatic malignancies? Which is the true, prevalence or incidence?

We read with great interest the article by Larghi et al. [1], a multicenter cohort study about prevalence and risk factors of extrapancreatic malignancies (EPMs) in patients with intraductal papillary mucinous neoplasm (IPMN) of the pancreas. They concluded that their prevalence was high, especially for colorectal carcinoma, renal cell and thyroid cancers. IPMN harbored some genetic mutations in the pancreas and was significantly associated with both synchronous and metachronous pancreatic cancer development [2, 3]. However, the relationship between IPMN and EPM still remained to be solved. There were some retrospective studies evaluating the prevalence of EPM in patients with IPMN and all of them, including the article by Larghi A et al., concluded that their prevalence was high. On the other hand, we reported the prospective study and concluded that the incidence of EPM in patients with IPMN was not high compared with that in general population in contrast to the high incidence of pancreatic cancers [4]. Prevalence is the proportion of a population found to have a disease, whereas incidence is a measure of the risk of developing a disease within a special period of time. The object to be measured was different between them, so it should be interpreted carefully. In focusing on the prevalence, overestimation of EPM could not be eliminated due to the diagnostic bias. As described in the article by Larghi et al. [1], incidence of EPM in their cohort was expected. Some patients with IPMN may have some germline mutations, like BRCA2 in the article by Lubezky et al. [5], but the majority did not. There were no significant risk factors for developing IPMN. Therefore, if IPMN was really associated with EPM, both the prevalence and incidence should be high. Until the high incidence of EPM in patients with IPMN or genetic mutations for developing EPM was to be elucidated, systemic surveillance should not be justified without certain specific risk factors for developing EPM.