Natural history of low-risk branch-duct intraductal papillary mucinous neoplasms and indeterminate pancreatic cysts: Implications on surveillance intervals by cyst size.

Background: The optimal surveillance strategy for low-risk branch-duct intraductal papillary mucinous neoplasms (BD-IPMN) remains unclear. We aim to evaluate the natural history of low-risk BD-IPMN/indeterminate pancreatic cysts to determine optimal surveillance intervals.

Methods: We conducted a retrospective cohort study of patients with radiologically-diagnosed low-risk BD-IPMN/indeterminate pancreatic cysts from 1998 to 2021 at a tertiary referral center. Low-risk BD-IPMN, worrisome features (WF) and high-risk stigmata (HRS) were defined as per existing guidelines. Patients were grouped into three categories based on cyst size at diagnosis: <10 mm, 10-19 mm and 20-29 mm. The size distribution and cumulative incidence of WF and HRS development were charted annually for the first five years.

Results: We studied 1668 patients, with 794 (47.6 %), 652 (39.1 %) and 222 (13.3 %) with cysts <10 mm, 10-19 mm and 20-29 mm at baseline respectively. Overall WF and HRS development was seen in 11.7 % and 1.4 % of patients respectively, with higher proportion of WF (6.8 vs 9.8 vs 34.7 %, p < 0.001) and HRS (0.9 vs 1.4 vs 3.6 %, p = 0.011) development with increasing baseline size category. Cysts <10 mm had 94.3 % < 30 mm at five years, 2.0 % WF at one year and a single case of HRS at two years. Cysts 10-19 mm had 94.7 % < 30 mm at five years, 2.2 % WF at one year and the first incident case of HRS at one year. Cysts 20-29 mm had 63.8 % < 30 mm at five years, 9.5 % WF and 1.1 % (4 cases) HRS by one year.

Conclusion: Baseline cyst size can be used to guide surveillance intervals for low-risk BD-IPMN/indeterminate pancreatic cysts.