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Long-Term Surveillance of One Thousand Side-Branch Intraductal Pancreatic Mucinous Neoplasms: Defining a Surveillance Strategy Based on Clinically-Relevant Progression
*Mir Shanaz Hossain1, *Chase J. Wehrle1, *Breanna Perlmutter1, *Jenny H. Chang1, *Hanna Hong1, *Robert Naples1, *Kathryn A. Stackhouse2, *John McMichael1, *Samer Naffouje3, *Daniel Joyce1, *Robert Simon1, *Toms Augustin3, R. Matthew Walsh1
1Digestive Diseases and Surgery Institute, Cleveland Clinic, Cleveland, OH; 2General Surgery, Cleveland Clinic Akron General, Akron, OH; 3General Surgery, Cleveland Clinic Fairview Hospital, Cleveland, OH

Objective: Side-branch intraductal papillary mucinous neoplasms (SB-IPMNs), are increasingly discovered incidentally, making identification of high-risk lesions essential to avoid unnecessary resections. We aim to quantify the rate of progression in surveilled cysts and assess what factors require resection.
Methods: A prospectively maintained database of presumed pancreatic cystic neoplasms was queried for patients with imaging or aspiration criteria for SB-IPMN. Patients surveilled with at least two cross-sectional abdominal imaging studies>6 months apart were included; those undergoing up-front resection were excluded. Clinically relevant progression (CR-Progression) was defined as development of worrisome or high-risk stigmata by the Fukuoka guidelines, or development of pancreatic cancer. Size growth>5mm in 2 years or growth to>3cm was considered CR-Progression while size>3cm on initial imaging was not.
Results: There were 1,334 patients diagnosed with SB-IPMN from 1997-2023. One-thousand (75.0%) had >6months surveillance while 33 (2.5%) underwent up-front surgery.
The rate of CR-progression was 15.8% (n=158) and was based on size increase (n=63, 6.3%), main-duct involvement (n=50, 5%), other Fukuoka criteria (n=28, 2.8%), or progression directly from low-risk to malignancy (n=17, 1.7%). Excluding cysts progressing directly to malignancy, those with clinically relevant progression developed cancer in 10.6% (n=14/131) and HGD in 9.2% (n=12/131); these rates were significantly higher than in the remainder of the surveilled cohort (n=14/842, 1.7%, p<0.001). The rate of malignancy during surveillance was 3.1% (n=31/1000) at a median follow-up of 6.6 years (IQR 3.0-10.26 years). Median time to CR-progression was 3.4years (IQR 1.7-6.4years).
FNA demonstrated a sensitivity=0.435 (95%CI 0.232-0.637), specificity=0.926 (0.827-1.02), positive predictive value=0.833 (0.625-1.04) and negative predictive value 0.658 (0.507-0.809) for cancer on final pathology.
There was no difference in the rate of malignancy in surveilled cysts based on initial size>3cm or <3cm (n=3/84, 3.6% vs n=28/913, 3.1%, p=0.572) during the median 6.6-year surveillance period. CR-progression was more frequent in cysts>3 cm at initial diagnosis (22.4% vs 15.4%, p=0.010). No cysts progressing directly to malignancy had initial size>3cm (n=0/17). HGD/malignancy was more common in cysts with worrisome or high-risk stigmata (n=6/17, 35.2%) or main-duct involvement (24%, n=12/50) versus growth in size (n=4/63, 6.3%, p=0.011) [Figure 1].
Conclusion: The rate of clinically relevant progression for SB-IPMNs is low but not insignificant based on long-term follow-up. A positive FNA has value in predicting the need for resection, though cysts with a negative FNA still require surveillance. Active surveillance should drive decision for resection rather than initial cyst size. Long-term non-operative surveillance is warranted, with surgery reserved for cysts with clinically relevant progression.

Figure 1. Progression of the Side Branch IPMN. Malignant/dysplastic potential of high-risk SB-IPMNs by the feature making them high risk. Main duct involvement and other non-size-based Fukuoka stigmata were associated with a higher rate of malignancy/high grade dysplasia than cysts deemed high-risk based on size criteria (p=0.011).
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