Branch-Duct Intraductal Papillary Mucinous Neoplasms Measuring Less than 10 mm Exhibit a Significantly Lower Risk of Developing “Worrisome Features”

Background: Pancreatic carcinomas are among the malignant tumours with the highest mortality and remain associated with an extremely poor prognosis. Early identification and surveillance of premalignant lesions, such as intraductal papillary mucinous neoplasms (IPMNs), are therefore of central importance for preventing malignant transformation. According to the revised Kyoto Guidelines, for small branch-duct IPMNs (BD-IPMNs) measuring less than 20 mm and lacking high-risk factors (“worrisome features”), regular diagnostic imaging is recommended. However, it remains unclear whether BD-IPMNs smaller than 10 mm carry a comparable risk of progression and therefore require monitoring at the same frequency. Methods: In this retrospective analysis, all patients who had undergone follow-up examinations for IPMN at St. Josef University Hospital Bochum between 1 January 2006 and 30 September 2025, were identified based on the coded ICD diagnoses K86.2 (“pancreatic cyst”) or D37.70 (“neoplasm of uncertain or unknown behaviour: pancreas”). Results: A total of 185 patients with BD-IPMN with a mean follow-up of 6.5 years and an average of 10 EUS examinations per patient were included in the final analysis. Overall, 37.8% developed at least one worrisome feature, whereas high-risk stigmata were rare (1.6%). Only one patient (0.5%) developed IPMN-associated pancreatic carcinoma during follow-up. Patients with BD-IPMNs <10 mm at initial EUS developed significantly fewer worrisome features compared with those measuring 10–20 mm (14.1% vs. 58.3%; p < 0.01). No patient in the <10 mm group developed high-risk stigmata. An initial size of 10–20 mm was associated with a 4.2-fold increased risk of developing worrisome features or high-risk stigmata compared with <10 mm lesions (adjusted OR 3.93). Surgical indications for pancreatic resection occurred significantly less frequently in patients with lesions <10 mm (8.1%) than in those with 10–20 mm (30.0%) (p < 0.01). Time to development of worrisome features was comparable between the <10 mm and 10–20 mm lesions (31.2 vs. 33.9 months). Conclusions: In summary, BD-IPMNs measuring <10 mm were associated with a markedly lower risk of developing worrisome features compared with larger lesions. Further large-scale studies are warranted to clarify whether prolonging surveillance intervals for small BD-IPMNs can be safely recommended.