Co-occurring IPMN and pancreatic cancer: the same or different? An overview from histology to molecular pathology

Mucinous cystic neoplasms and simple mucinous cysts are two distinct precursors of pancreatic cancer: clinicopathological, genomic, and transcriptomic characterization

Mucinous cystic neoplasms (MCNs) of the pancreas are macroscopic precursors of pancreatic cancer. A similar cystic lesion but lacking the ovarian-type subepithelial stroma has been recently defined as a simple mucinous cyst (SMC); however, its nature remains unclear. This study aims to define the clinicopathological and molecular profiles of a cohort of MCNs and SMCs of the pancreas and their associated invasive carcinoma. Overall, 23 cases were identified, comprising 19 MCNs and 4 SMCs with co-occurring invasive carcinoma. A multiregional (two samples from each cystic lesion and one from the adenocarcinoma) DNA and RNA sequencing approach was used. The key findings can be summarized as follows: (1) Molecular association: In 22/23 cases (95.7%), the concomitant mucinous cyst and invasive carcinoma shared specific genomic alterations, establishing for the first time that SMC is a true precursor of pancreatic cancer. (2) Clinical behavior: carcinomas arising from SMC appeared to be more aggressive than those arising from MCN. (3) Mutational profile: both cyst types showed significant similarities to conventional pancreatic ductal adenocarcinoma (PDAC), with KRAS and TP53 the most commonly altered genes. (4) Intracystic heterogeneity: while most molecular alterations were present in both analyzed cystic areas, RNF43 showed the highest heterogeneity. (5) CDKN2A: its alterations were predominantly restricted to the invasive component, suggesting a role in driving the invasion in a subset of cases. CNKN2A may also serve as a potential biomarker for identifying high-risk cysts. (6) RNAseq: most cases showed a switch from the classical to the basal transcriptome subtype during the progression from cystic neoplasms to invasive cancers. These findings establish SMCs as new precursors of pancreatic cancer and provide critical insights into the tumorigenesis of MCNs, with potential immediate implications for tumor taxonomy and clinical management. © 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Older Age as a Worrisome Feature in Patients With Intraductal Papillary Mucinous Neoplasms: A Long-Term Surveillance Study

INTRODUCTION

Aging has been implicated in the development of various cancer types. No study has specifically investigated age at intraductal papillary mucinous neoplasm (IPMN) diagnosis in relation to the long-term risk of pancreatic carcinogenesis.

METHODS

Within a prospective cohort of 4,104 patients diagnosed with pancreatic cysts, we identified 3,142 patients with IPMNs and examined an association of age at IPMN diagnosis with the incidence of pancreatic carcinoma. Using the multivariable competing-risks proportional hazards regression model, we estimated subdistribution hazard ratios (SHRs) and 95% confidence intervals (CIs) for pancreatic carcinoma incidence according to age at IPMN diagnosis.

RESULTS

During 22,187 person-years of follow-up, we documented 130 patients diagnosed with pancreatic carcinoma (64 with IPMN-derived carcinoma and 66 with concomitant ductal adenocarcinoma). Older age at IPMN diagnosis was associated with a higher risk of pancreatic cancer incidence ( Ptrend = 0.002). Compared with patients younger than 55 years, patients aged 55-64, 65-74, and ≥ 75 years had adjusted SHRs of 1.80 (95% CI, 0.75-4.32), 2.56 (95% CI, 1.10-5.98), and 3.31 (95% CI, 1.40-7.83), respectively. Patients aged 70 years and older had a numerically similar adjusted SHR compared with patients younger than 70 years with worrisome features defined by the international consensus guidelines (1.73 [95% CI, 1.01-2.97] and 1.66 [95% CI, 0.89-3.10], respectively).

DISCUSSION

Older patients with IPMNs were at a higher risk of developing pancreatic carcinoma during surveillance. Surgically fit elderly patients may be good candidates for periodic surveillance aimed at a reduction of pancreatic cancer-related deaths.

Risk factors for pancreatic cancer in individuals with intraductal papillary mucinous neoplasms and no high-risk stigmata during up to 5 years of surveillance: a prospective longitudinal cohort study

BACKGROUND

Cyst size, its growth rate, and diameter of the main pancreatic duct (MPD) are all associated with pancreatic carcinoma prevalence in intraductal papillary mucinous neoplasms (IPMNs).

OBJECTIVE

To examine the above factors in relation to future risk of incident pancreatic carcinoma in individuals with IPMNs harbouring no high-risk stigmata.

DESIGN

In a prospective longitudinal cohort, we analysed 2549 patients with IPMNs. A multivariable cause-specific Cox proportional hazards regression model was built to estimate HRs for incident pancreatic carcinoma.

RESULTS

IPMN size at baseline and its annual growth rate over 2 years of follow-up were associated with incident pancreatic carcinoma (ptrend<0.001). The multivariable cause-specific HR per 10 mm increase in IPMN size was 1.28 (95% CI 1.10 to 1.50). The annual growth rates of 1.5-2.4 mm/year and ≥2.5 mm/year over 2 years were associated with multivariable cause-specific HRs of 1.91 (95% CI 0.78 to 4.67) and 4.52 (95% CI 2.28 to 8.98), respectively (vs <1.5 mm/year). Neither IPMN size at 5 years nor its maximum growth rate during 5 years was associated with incident pancreatic carcinoma (ptrend>0.07). MPD diameter at 5 years was associated with incident pancreatic carcinoma (multivariable cause-specific HR per 2 mm increase, 2.12; 95% CI 1.72 to 2.63). A predictive nomogram was generated for calculating the risk of incident pancreatic carcinoma.

CONCLUSION

IPMN size and its growth rate predict future pancreatic carcinoma risk only during first 5 years of follow-up. MPD diameter at 5 years may identify patients who still harbour a high risk for pancreatic carcinoma.

The Revised Kyoto Criteria and Risk of Malignancy Among Patients With Intraductal Papillary Mucinous Neoplasms

BACKGROUND & AIMS

The revised Kyoto guidelines have a new catalog of high-risk stigmata and worrisome features for the risk stratification of intraductal papillary mucinous neoplasms (IPMNs). We aimed to validate the stratification system in terms of short- and long-term risks of pancreatic carcinoma.

METHODS

We included 3336 patients diagnosed with IPMNs in 2000-2021 and examined short-term (≤6 months) and long-term risks of pancreatic carcinoma diagnosis. We used the multivariable competing-risks proportional hazards regression model to calculate subdistribution hazard ratios for long-term incidence of pancreatic carcinoma with adjustment for potential confounders.

RESULTS

In short-term analyses, pancreatic carcinomas were prevalent predominantly in IPMNs with high-risk stigmata (49% vs 1.3% and 0.05% in IPMNs with worrisome features and no risk factors, respectively). In long-term analyses of worrisome features, the main pancreatic duct diameter of 5-9.9 mm, acute pancreatitis, and IPMN growth rate of 2.5 mm/y were associated with a high incidence with multivariable subdistribution hazard ratios of 3.46 (95% confidence interval [CI], 2.04-5.89), 5.65 (95% CI, 1.86-17.2), and 3.83 (95% CI, 2.14-6.86), respectively. An increasing number of worrisome features at baseline was associated with a higher prevalence and incidence of pancreatic carcinoma (Ptrend < .001). Patients with 1, 2, and 3-4 worrisome features had multivariable subdistribution hazard ratios for pancreatic cancer incidence of 1.43 (95% CI, 0.93-2.19), 2.17 (95% CI, 1.17-4.05), and 10.1 (95% CI, 4.20-24.5), respectively (vs no positive feature).

CONCLUSIONS

The revised Kyoto criteria stratify IPMN patients well in terms of the short- and long-term risks of pancreatic carcinoma diagnosis, potentially informing personalized patient management.

PanIN or IPMN? Redefining Lesion Size in 3 Dimensions

Pancreatic ductal adenocarcinoma (PDAC) develops from 2 known precursor lesions: a majority (∼85%) develops from pancreatic intraepithelial neoplasia (PanIN), and a minority develops from intraductal papillary mucinous neoplasms (IPMNs). Clinical classification of PanIN and IPMN relies on a combination of low-resolution, 3-dimensional (D) imaging (computed tomography, CT), and high-resolution, 2D imaging (histology). The definitions of PanIN and IPMN currently rely heavily on size. IPMNs are defined as macroscopic: generally >1.0 cm and visible in CT, and PanINs are defined as microscopic: generally <0.5 cm and not identifiable in CT. As 2D evaluation fails to take into account 3D structures, we hypothesized that this classification would fail in evaluation of high-resolution, 3D images. To characterize the size and prevalence of PanINs in 3D, 47 thick slabs of pancreas were harvested from grossly normal areas of pancreatic resections, excluding samples from individuals with a diagnosis of an IPMN. All patients but one underwent preoperative CT scans. Through construction of cellular resolution 3D maps, we identified >1400 ductal precursor lesions that met the 2D histologic size criteria of PanINs. We show that, when 3D space is considered, 25 of these lesions can be digitally sectioned to meet the 2D histologic size criterion of IPMN. Re-evaluation of the preoperative CT images of individuals found to possess these large precursor lesions showed that nearly half are visible on imaging. These findings demonstrate that the clinical classification of PanIN and IPMN fails in evaluation of high-resolution, 3D images, emphasizing the need for re-evaluation of classification guidelines that place significant weight on 2D assessment of 3D structures.

Molecular Pathology of Pancreatic Cystic Lesions with a Focus on Malignant Progression

The malignant progression of pancreatic cystic lesions (PCLs) remains understudied with a knowledge gap, yet its exploration is pivotal for effectively stratifying patient risk and detecting cancer at its earliest stages. Within this review, we delve into the latest discoveries on the molecular level, revealing insights into the IPMN molecular landscape and revised progression model, associated histologic subtypes, and the role of inflammation in the pathogenesis and malignant progression of IPMN. Low-grade PCLs, particularly IPMNs, can develop into high-grade lesions or invasive carcinoma, underscoring the need for long-term surveillance of these lesions if they are not resected. Although KRAS and GNAS remain the primary oncogenic drivers of neoplastic development in IPMNs, additional genes that are important in tumorigenesis have been recently identified by whole exome sequencing. A more complete understanding of the genes involved in the molecular progression of IPMN is critical for effective monitoring to minimize the risk of malignant progression. Complicating these strategies, IPMNs are also frequently multifocal and multiclonal, as demonstrated by comparative molecular analysis. Algorithms for preoperative cyst sampling and improved radiomic techniques are emerging to model this spatial and temporal genetic heterogeneity better. Here, we review the molecular pathology of PCLs, focusing on changes associated with malignant progression. Developing models of molecular risk stratification in PCLs which can complement radiologic and clinical features, facilitate the early detection of pancreatic cancer, and enable the development of more personalized surveillance and management strategies are summarized.

Gene Rearrangement and Expression of PRKACA and PRKACB Govern Morphobiology of Pancreatobiliary Oncocytic Neoplasms

Intraductal oncocytic papillary neoplasms (IOPNs) are distinct from intraductal papillary mucinous neoplasms based on characteristic morphologic and genetic features represented by fusion genes involving PRKACA or PRKACB (PRKACA/B). However, pancreatic and biliary tumors with partial oncocytic features are often encountered clinically, and their molecular features are yet to be clarified. This study included 80 intraductal papillary neoplasms: 32 tumors with mature IOPN morphology (typical), 28 with partial or subclonal oncocytic features (atypical), and 20 without oncocytic features (control). We analyzed PRKACA/B fusion genes, including ATP1B1::PRKACA, DNAJB1::PRKACA, and ATP1B1::PRKACB, by reverse-transcription PCR; mRNA expression of fusion genes and nonrearranged PRKACA/B genes by quantitative reverse-transcription PCR; mutations in KRAS, BRAF, and GNAS by targeted sequencing or droplet digital PCR; and the expression of cyclic adenosine monophosphate (cAMP)-dependent protein kinase catalytic subunits α (PRKACA) and β (PRKACB), phosphorylated cAMP response element-binding protein, and aberrations of p16, p53, SMAD4, STK11, and β-catenin by immunohistochemistry. PRKACA/B fusion genes were detected in 100% (32/32) of typical, 46% (13/28) of atypical, and 0% (0/20) of control (P < .05). Expression of PRKACA, PRKACB, and phosphorylated cAMP response element-binding protein was upregulated in neoplasms with PRKACA/B fusion genes (P < .05). mRNA expression of the PRKACA/B fusion genes and protein expression of PRKACA or PRKACB tended to be higher in typical than in atypical cases (mRNA, P = .002; protein expression, P = .054). In some atypical neoplasms with mixed subtypes, PRKACA/B fusion genes were superimposed exclusively on oncocytic components. Typical IOPNs harbored fewer KRAS and GNAS mutations than control samples and fewer alterations in p53 and STK11 than atypical samples (P < .05). In conclusion, PRKACA/B fusion genes not only are the characteristic drivers of IOPNs but also play a crucial role in the development of subclonal oncocytic neoplasms. Moreover, oncocytic morphology is strongly associated with upregulation of PRKACA/B, which may provide clues for potential therapeutic options.