The marked increase in the diagnosis of intraductal papillary mucinous neoplasm over the last 2 decades is primarily due to a striking rise in the number of IPMNs identified incidentally, Dr. David A. Klibansky and his colleagues reported in the May issue of Clinical Gastroenterology and Hepatology.
The researchers compared the estimated number of all IPMNs against the number of malignant IPMNs reported to the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) database and found that the incidence of nonmalignant IPMN is 70 times higher than that of malignant IPMN.
"It would seem likely that we are recognizing an increasing number of pancreatic cystic lesions whose natural history may not be clinically important," the authors wrote. And these lesions are being found chiefly because of the widespread use of imaging, particularly high-resolution cross-sectional imaging.
Yet identifying these benign IPMNs still "drives referral to specialists, years of surveillance imaging, invasive testing, and possibly even surgical intervention because of heightened concern over malignant potential," said Dr. Klibansky of the gastroenterology and hepatology section at Dartmouth-Hitchcock Medical Center, Lebanon, N.H., and his associates (Clin. Gastro. Hepatol. 2012 [doi: 10.1016/j.cgh.2011.12.029]).
Since there is no database from which to derive the national incidence of IPMN, the researchers attempted to estimate that incidence by using data from a previously published, well-defined population study: the Rochester Epidemiology Project index, which "includes the records of virtually all medical providers that care for the residents of Olmsted County, Minnesota."
For this study, the clinical, radiographic, and pathologic data were reviewed for all 28 cases of IPMN treated during 1984-2007. The national incidence of the disease was then calculated by dividing the number of incident cases by the number of person-years at risk for the population, standardized to the age and sex distribution of the U.S. white population in the year 2000.
The investigators found that there was a 14-fold increase in the age- and sex-adjusted incidence of IPMN between 1985 and 2005, from 0.31 to 4.35 cases per 100,000 persons. A large increase in incidence has long been suspected and has been demonstrated in some previous studies, Dr. Klibansky and his associates wrote.
These figures were then compared with rates of IPMN-related cancer as estimated by SEER data during the same time period. The first malignant IPMN was reported to the SEER database in 2000.
"Using the most recent shared data point of 2005," the researchers found that the incidence of nonmalignant IPMN was 68.5 times higher than that of malignant IPMN.
Data from the early literature on IPMN, derived predominantly from retrospective analysis of surgical series, suggested that cancerous lesions accounted for 60%-70% of resected IPMN specimens from the main duct and 25% of those from branch ducts. "This literature, while critically important and representative of some of the seminal work in the evaluation of IPMN, is potentially biased with overrepresentation of malignant disease," given that these early patients were likely to have had symptomatic disease or larger than usual lesions, Dr. Klibansky and his colleagues noted.
Their study "is not meant to undermine the importance of identifying and treating IPMN that are high risk to harbor or develop malignancy," the investigators stressed.
It does, however, highlight the need for ways to differentiate IPMN that require intervention from those that require only surveillance and those that are so low risk that they require no further follow-up.
Most incidentally identified IPMNs do not meet the criteria for surgical resection, and current guidelines recommend only frequent surveillance using high-resolution imaging. The findings of this and other studies suggest that malignant transformation of such lesions is low and that even this recommended surveillance is unnecessarily aggressive and possibly unwarranted.
But many patients as well as clinicians pursue further, invasive evaluation and even surgical removal because of concern over the malignant potential of even small, asymptomatic pancreatic cysts, Dr. Klibansky and his associates said.
Physicians can reassure patients that the 5-year survival for even invasive IPMN "is significantly better than that of traditional ductal adenocarcinoma," they suggested. Moreover, "in a patient population that is older and likely to harbor significant medical comorbidities, a careful risk-to-benefit analysis needs to be performed on a case-by-case basis, taking into consideration the likely impact IPMN will have on a given patient’s life versus morbidity and costs related to intervention or lifelong surveillance," the researchers said.
This study was funded in part by the National Institutes of Health. No financial conflicts were reported.