Patients with branch duct intraductal papillary mucinous neoplasms were about 19 times more likely to develop malignancies over 5 years compared with the general population, although they lacked worrisome features of malignancy at baseline.

The overall risk of malignancy in this cohort approached 8% and persisted for 10 years or more, said Ilaria Pergolini, MD, of Massachusetts General Hospital, Boston, and her associates. The findings support surveillance of this population past 5 years, although cysts that remain 1.5 cm or smaller for more than 5 years might be regarded as unlikely to become malignant, they wrote. The report appears in the November issue of Gastroenterology ( doi: 10.1053/j.gastro.2017.07.019 ).

Few studies have explored branch duct intraductal papillary mucinous neoplasms (BD-IPMNs), which the researchers defined as unilocular or multilocular pancreatic cysts with a nondilated main pancreatic duct (smaller than 5 mm). To begin filling this gap, they retrospectively studied 577 patients with suspected or presumed BD-IPMNs followed at Massachusetts General Hospital. Patients underwent cross-sectional imaging 3 months or more after initial diagnosis at least once thereafter. Standardized incidence ratios were calculated based on population-level data for the United States from the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) program.

Patients tended to be in their mid-60s at diagnosis (range, 21-90 years) and 59% were female, said the researchers. Median follow-up time was 82 months and ranged between 6 and 329 months, but 63% of patients were followed for at least 5 years (median, 107 months), and about one in five were followed for more than a decade. Fully 83% of patients were asymptomatic at initial diagnosis, of which 10% subsequently became symptomatic. Most patients underwent diagnostic CT, but nearly half underwent MRI/MRCP and about a third underwent endoscopic ultrasound. At diagnosis, median cyst size was 14 mm (range, 2-54 mm) and 9% of patients had cysts measuring at least 3 cm. By the end of follow-up, 55% had larger cysts than at baseline, and cysts grew by a median of 0.9 mm per year.

At diagnosis, only 1% of patients had high-risk stigmata while 12% had worrisome features such as acute pancreatitis, cysts measuring at least 3 cm, thickened or enhancing cyst walls, nonenhancing mural nodules, main pancreatic duct size of 5-9 mm, an abrupt change in caliber of the main pancreatic duct, and lymphadenopathy. During follow-up, another 13% of patients developed new worrisome features and 9% developed high-risk stigmata, while 2% experienced regression of a nodule. In all, 36% of patients had cysts with either worrisome features, high-risk stigmata, or both at some point during the study.

Among 363 patients followed for at least 5 years, 20 (5.5%) were diagnosed with high-risk dysplasia or invasive neoplasms and 4.4% developed invasive cancer, for a standardized incidence ratio of 18.8 (95% confidence interval, 9.7-32.8; P less than .001). Among 108 patients who had cysts measuring 1.5 cm or less, only one individual developed a distinct ductal adenocarcinoma during 5 or more years of follow-up. But of 255 patients with larger cysts, the 5-year rate of malignancy was 7.5% (P = .01).

“The absence of worrisome features or high-risk stigmata at a 5-year time point does not exclude the development of pancreatic malignancy, and the risk in these patients is 18.8 times higher than that of the general population,” the researchers concluded. “Because of this, we strongly support continued surveillance after 5 years from the initial diagnosis.” Cysts that remain 1.5 cm or smaller for at least 5 years are probably low risk, they said. “This is an important issue for further investigation, since it may help reduce costs related to surveillance and improve patients’ quality of life.”

The investigators did not disclose external funding sources. They reported having no conflicts of interest.