We describe 2 striking histologic changes in pancreata surgically resected from patients with a strong family history of pancreatic cancer. First, these pancreata are remarkable for multiple precursor lesions, including PanIN lesions, involving as many as 27.3% of the duct profiles in a single distal pancreatectomy. Second, the precursor lesions in these pancreata, even the low-grade PanIN-1 lesions, were often directly associated with lobular atrophy of the surrounding pancreatic parenchyma. The latter association was also present, although much more focally, in the controls.
The number of PanINs identified in the cases with a strong family history of pancreatic cancer was remarkably high. All 8 cases contained PanINs, a total of 273 PanIN profiles were identified in the cases (mean 34 PanIN profiles per resected portion of pancreas), and the density of PanIN profiles in the cases was significantly greater than that observed in age-matched controls (P<0.01). These multiple PanIN profiles represent multifocal disease as demonstrated by the distinct KRAS gene mutations identified in separately microdissected precursor lesions from 2 of the patients.
The finding of such a high density of multifocal precursor lesions in a single pancreas suggests that the portion of the gland not resected in these individuals retains a significantly increased risk of developing an invasive pancreatic cancer. Although one might argue that these patients would benefit from a total pancreatectomy, the benefit of such surgery is unproven, whereas the risks are real. A patient has been reported who died after a prophylactic total pancreatectomy, and all patients who undergo a total pancreatectomy develop brittle diabetes mellitus.6
Therefore, short of total pancreatectomy, our recommendation for the patients in this series with multiple precursor lesions has been continued surveillance of the pancreatic remnant, using EUS and CT or magnetic resonance cholangiopancreatography.
The distinctive pattern of lobular atrophy associated with PanINs observed in the pancreata in this study has also been reported focally in elderly patients by Detlefsen et al13
and diffusely in patients with a strong family history of pancreatic cancer by Meckler et al.41
Meckler et al41
concluded that the “dysplasia appeared to develop within the microcystically dilated intralobular glands and ducts.” This conclusion suggested that the familial pancreatic cancer gene could be a pancreatitis-inducing or cyst-inducing gene. When compared to findings in animal models, however, the morphology of lobular atrophy observed in all 3 series of patients suggests that it is the epithelial precursor lesions that are causing the parenchymal atrophy and duct dilatation. 13
Surgical obstruction of the pancreatic duct in animal models causes a stereotypic series of changes in the pancreas and these are the very same alterations identified in the pancreata in all 3 series of patients.2,4,5,10,30,35,44,52,54
The first change after experimental ligation of the pancreatic duct in animal models is a thinning of the acinar cells with a loss of the apical granular cytoplasm and retention of the basal basophilic cytoplasm. 10,44,54
This acinar cell thinning is associated with slight dilatation of the acinar lumina (compare with ). The acinar cells then die through the processes of necrosis and apoptosis.19,52
Acinar cell loss progresses over time until only a few cells with granular eosinophilic cytoplasm remain, and eventually it is difficult to distinguish between ductal cells and acinar cells (compare with ). In the end stages, there is a marked acinar dropout such that essentially no acinar cells remain (compare with ). The lobular units are then composed of a central, slightly dilated duct surrounded by aggregates of islets of Langerhans and embedded in fibro-fatty connective tissue.30
The histologic changes reported here (), by Detlefsen et al, and by Meckler et al are essentially phenocopies of these features seen in animal models of pancreatic duct ligation.41
It therefore seems that it is not the atrophy that is causing the PanINs to develop, but rather that it is the PanINs which develop first, producing multiple foci of small duct obstruction, in turn progressing to multifocal lobulocentric atrophy.13
The initial event in some forms of familial pancreatic cancer therefore seems to be the development of multiple intraductal neoplasms (PanINs and IPMNs). By analogy with FAP, this pattern of epithelial neoplasia suggests that some cases of familial pancreatic cancer are caused by mutations in a gatekeeper gene.27,28
Gatekeeper genes are genes that directly regulate the emergence of incipient neoplasms by exerting control over stem cell numbers,34
promoting senescence, or perhaps by inhibiting cell proliferation or promoting cell death. In the original gatekeeper models of neoplasia,24,25,49
only one mutation, in addition to the germline mutation, is needed to initiate neoplasia. If an inherited mutation in a gatekeeper gene is recessive, the lesions are focal, rather than diffuse, and the second hit occurs in the second allele of the gatekeeper gene. Examples of gatekeeper genes include the RB, VHL, NF1, MEN1
, and APC
genes. Inactivation of a gatekeeper gene tends to lead to a very specific tissue distribution of cancer, and individuals with an inherited mutation in a gatekeeper gene have as much as a 103
increased risk of developing cancer.27,28
The cases in this study with multiple precursor lesions thus reasonably fit the characteristics of inherited mutations in a recessive gatekeeper gene.
The striking association we observed between precursor lesions (PanINs and IPMNs) and obstructive changes in the pancreatic parenchyma correlates with chronic pancreatitis-like changes observed radiologically in these patients (). Chronic pancreatitis-like changes, including chronic pancreatitis-like abnormalities of the ducts (ectasia, irregularity, saccules) and parenchyma (heterogeneity, lobularity), were observed by EUS and by endoscopic retrograde cholangiopancreatography (ERCP) in two-thirds of the 109 patients screened in CAPS 1 and CAPS 2.7,8
These changes correlate with markers of neoplasia including abnormal DNA methylation in the pancreatic juice,40
and were significantly more common and more severe in individuals from familial pancreatic cancer kindreds than in controls, even after adjusting for age and alcohol exposure.8
Similar changes have also been reported by others in patients with a strong family history of pancreatic cancer.6
Brentnall et al6
screened 14 patients with a strong family history of pancreatic cancer using a combination of EUS, ERCP, and spiral computed tomography. Nine of these 14 were found to have heterogenous pancreatic parenchyma on EUS and 8 had ERCP changes including irregular and poor duct filling, and ectactic ducts with saccules. The histologic changes of lobular parenchymal atrophy we describe correlate with the heterogenous pancreatic parenchyma seen on EUS, whereas the precursor lesions themselves, particularly the small IPMNs, explain the irregular and poor duct filling, and the ectactic ducts seen by ERCP.
These observations therefore provide a morphologic basis to an approach to screening for early pancreatic neoplasia, particularly multifocal intraductal precursors of the type seen in familial pancreatic cancer. Multifocal PanINs and IPMNs will produce multiple foci of atrophy and cyst formation scattered in a background of intact pancreatic parenchyma. This heterogeneous pattern of atrophy will produce, as observed in the current study, and in the patients reported by Brentnall et al, a heterogeneous pattern on EUS. This heterogeneity can be quantified using the standard deviation of the gray-scale distribution (pixel densities) of the B-mode sonographic image.43
Indeed, Morita et al reported that the mean brightness and standard deviation derived from the gray-scale histogram increase after pancreatic duct ligation in dogs.43
Simply put, although the precursor lesions may be too small to visualize by currently available imaging technologies, the effects they produce on the pancreatic parenchyma can be detected and quantified.
Although the data do not allow us to draw conclusions about the optimal age at which to begin screening high-risk patients for pancreatic cancer, the observation that the number of PanIN profiles in the cases increased significantly with patient age (r=0.81, P<0.015) suggests that age should be strongly factored into any screening program.
At first glance it would seem that intraductal precursor lesions produce the lobular parenchymal atrophy by physically obstructing the affected duct. The atrophic changes were, however, observed even in association with flat, low-grade lesions (). The epithelial cells of the lesions clearly do not obstruct the lumen, suggesting that other mechanisms may contribute to the atrophy observed. For example, mucins and aquaporins are known to be abnormally expressed in PanINs, and their expression could alter the viscosity of intraluminal secretions causing a relative reduction in their flow.26,37,45,46
Alternatively, the precursor lesions could aberrantly express proteins which prematurely activate proteases such as trypsinogen.45
The premature activation of trypsinogen has been shown to play a role in the development of obstructive atrophy in the pancreas,42
and PanINs are known to ectopically express a number of proteins.45
For example, the expression of even a small amount of enterokinase on the surface of PanINs could prematurely activate trypsinogen, initiating a cascade of enzyme activation that leads to atrophy.
Finally, our findings suggest that a vicious cycle may develop in the pancreata of patients with a strong family history of pancreatic cancer. We have shown that the precursor lesions cause lobular chronic pancreatitis. The resultant episodes of tissue injury and repair may disrupt homeostatic mechanisms that govern stem cell regulation, furthering neoplastic progression, which would in turn produce more lobular chronic pancreatitis, continuing the vicious cycle.3,11,23
In summary, some patients with a strong family history of pancreatic cancer develop numerous noninvasive epithelial precursor lesions including PanINs and IPMNs. These lesions are associated with lobular atrophy of the pancreatic parenchyma. The multifocality of the precursor lesions suggests that an inherited mutation of a gatekeeper gene is responsible for some cases of familial pancreatic cancer. The lobular atrophy associated with these precursor lesions provides an explanation for the chronic pancreatitis-like changes seen in these pancreata, and the patchy nature of this atrophy suggests an approach for screening for early pancreatic neoplasia in at-risk individuals.