Abnormalities of the RB1 and DCC tumor suppressor genes: uncommon in human pancreatic adenocarcinoma

Does the WHO 2010 classification of pancreatic neuroendocrine neoplasms accurately characterize pancreatic neuroendocrine carcinomas?

BACKGROUND

The WHO classified pancreatic neuroendocrine neoplasms in 2010 as G1, G2, and neuroendocrine carcinoma (NEC), according to the Ki67 labeling index (LI). However, the clinical behavior of NEC is still not fully studied. We aimed to clarify the clinicopathological and molecular characteristics of NECs.

METHODS

We retrospectively evaluated the clinicopathological characteristics, KRAS mutation status, treatment response, and the overall survival of eleven pNEC patients diagnosed between 2001 and 2014 according to the WHO 2010. We subclassified WHO-NECs into well-differentiated NEC (WDNEC) and poorly differentiated NEC (PDNEC). The latter was further subdivided into large-cell and small-cell subtypes.

RESULTS

The median Ki67 LI was 69.1% (range 40-95%). Eleven WHO-NECs were subclassified into 4 WDNECs and 7 PDNECs. The latter was further separated into 3 large-cell and 4 small-cell subtypes. Comparisons of WDNEC vs. PDNEC revealed the following traits: hypervascularity on CT, 50% (2/4) vs. 0% (0/7) (P = 0.109); median Ki67 LI, 46.3% (40-53%) vs. 85% (54-95%) (P = 0.001); Rb immunopositivity, 100% (4/4) vs. 14% (1/7) (P = 0.015); KRAS mutations, 0% (0/4) vs. 86% (6/7) (P = 0.015); response rates to platinum-based chemotherapy, 0% (0/2) vs. 100% (4/4) (P = 0.067), and median survival, 227 vs. 186 days (P = 0.227).

CONCLUSIONS

The WHO-NEC category may be composed of heterogeneous disease entities, namely WDNEC and PDNEC. These subgroups tended to exhibit differing profiles of Ki67 LI, Rb immunopositivity and KRAS mutation, and distinct response to chemotherapy. Further studies for the reevaluation of the current WHO 2010 classification are warranted.

Small cell and large cell neuroendocrine carcinomas of the pancreas are genetically similar and distinct from well-differentiated pancreatic neuroendocrine tumors

Poorly differentiated neuroendocrine carcinomas (NECs) of the pancreas are rare malignant neoplasms with a poor prognosis. The aim of this study was to determine the clinicopathologic and genetic features of poorly differentiated NECs and compare them with other types of pancreatic neoplasms. We investigated alterations of KRAS, CDKN2A/p16, TP53, SMAD4/DPC4, DAXX, ATRX, PTEN, Bcl2, and RB1 by immunohistochemistry and/or targeted exomic sequencing in surgically resected specimens of 9 small cell NECs, 10 large cell NECs, and 11 well-differentiated neuroendocrine tumors (PanNETs) of the pancreas. Abnormal immunolabeling patterns of p53 and Rb were frequent (p53, 18 of 19, 95%; Rb, 14 of 19, 74%) in both small cell and large cell NECs, whereas Smad4/Dpc4, DAXX, and ATRX labeling was intact in virtually all of these same carcinomas. Abnormal immunolabeling of p53 and Rb proteins correlated with intragenic mutations in the TP53 and RB1 genes. In contrast, DAXX and ATRX labeling was lost in 45% of PanNETs, whereas p53 and Rb immunolabeling was intact in these same cases. Overexpression of Bcl-2 protein was observed in all 9 small cell NECs (100%) and in 5 of 10 (50%) large cell NECs compared with only 2 of 11 (18%) PanNETs. Bcl-2 overexpression was significantly correlated with higher mitotic rate and Ki67 labeling index in neoplasms in which it was present. Small cell NECs are genetically similar to large cell NECs, and these genetic changes are distinct from those reported in PanNETs. The finding of Bcl-2 overexpression in poorly differentiated NECs, particularly small cell NEC, suggests that Bcl-2 antagonists/inhibitors may be a viable treatment option for these patients.

miR-132 and miR-212 are increased in pancreatic cancer and target the retinoblastoma tumor suppressor

Numerous microRNAs (miRNAs) are reported as differentially expressed in cancer, however the consequence of miRNA deregulation in cancer is unknown for many miRNAs. We report that two miRNAs located on chromosome 17p13, miR-132 and miR-212, are over-expressed in pancreatic adenocarcinoma (PDAC) tissues. Both miRNAs are predicted to target the retinoblastoma tumor suppressor, Rb1. Validation of this interaction was confirmed by luciferase reporter assay and western blot in a pancreatic cancer cell line transfected with pre-miR-212 and pre-miR-132 oligos. Cell proliferation was enhanced in Panc-1 cells transfected with pre-miR-132/-212 oligos. Conversely, antisense oligos to miR-132/-212 reduced cell proliferation and caused a G(2)/M cell cycle arrest. The mRNA of a number of E2F transcriptional targets were increased in cells over expressing miR-132/-212. Exposing Panc-1 cells to the β2 adrenergic receptor agonist, terbutaline, increased the miR-132 and miR-212 expression by 2- to 4-fold. We report that over-expression of miR-132 and miR-212 result in reduced pRb protein in pancreatic cancer cells and that the increase in cell proliferation from over-expression of these miRNAs is likely due to increased expression of several E2F target genes. The β2 adrenergic pathway may play an important role in this novel mechanism.

Biological approaches to therapy of pancreatic cancer

Pancreatic cancer is a lethal disease and notoriously difficult to treat. Only a small proportion is curative by surgical resection, whilst standard chemotherapy for patients with advanced disease has only modest effect with substantial toxicity. Clearly there is a need for the continual development of novel therapeutic agents to improve the current situation. Improvement of our understanding of the disease has generated a large number of studies on biological approaches targeting the molecular abnormalities of pancreatic cancer, including gene therapy and signal transduction inhibition, antiangiogenic and matrix metalloproteinase inhibition, oncolytic viral therapy and immunotherapy. This article provides a review of these approaches, both investigated in the laboratories and in subsequent clinical trials.

Molecular biology of exocrine pancreatic cancer

Exocrine pancreatic cancer is one of the neoplasias with a worse prognosis, with conventional treatments having little impact on disease outcome. Research and genomic high-throughput technology is continuously expanding our knowledge of pancreas cancer biology. Characterization of genetic and epigenetic alterations in pancreatic tumors has allowed a better understanding of the progression model of the disease at the molecular level. The development of new therapeutic approaches with target- oriented agents is been tested in the preclinical and clinical settings. This review updates the current available data on pancreatic cancer molecular biology.

Gene therapy developments for pancreatic cancer

Treatment options for pancreatic cancer have limited success and it is therefore an appropriate target for the development of new strategies, including gene therapy. Gene therapy approaches include inhibition of activated oncogenes (KRAS, LSM1) with antisense and RNA interference strategies, replacement of inactivated tumour suppressor genes (TP53, CDKN2A, CDKN1A), targeting of cell signalling pathways, gene-directed prodrug-activation therapies and the use of replication-competent oncolytic viruses. Angiogenesis and apoptosis have also been targeted for gene therapy. Clinical trials of gene therapy have shown only moderate anti-tumour effects. As there are many genetic abnormalities in pancreatic cancer, strategies combining different targets or indeed different modalities of treatment, may be more successful. Identification of new targets and improvements in delivery and targeting may further improve the efficacy of gene therapy in pancreatic cancer.

Modulation of cell cycle and gene expression in pancreatic tumor cell lines by methionine deprivation (methionine stress): implications to the therapy of pancreatic adenocarcinoma

The effect of methionine deprivation (methionine stress) on the proliferation, survival, resistance to chemotherapy, and regulation of gene and protein expression in pancreatic tumor lines is examined. Methionine stress prevents successful mitosis and promotes cell cycle arrest and accumulation of cells with multiple micronuclei with decondensed chromatin. Inhibition of mitosis correlates with CDK1 down-regulation and/or inhibition of its function by Tyr(15) phosphorylation or Thr(161) dephosphorylation. Inhibition of cell cycle progression correlates with loss of hyperphosphorylated Rb and up-regulation of p21 via p53 and/or transforming growth factor-beta (TGF-beta) activation depending on p53 status. Although methionine stress-induced toxicity is not solely dependent on p53, the gain in p21 and loss in CDK1 transcription are more enhanced in wild-type p53 tumors. Up-regulation of SMAD7, a TGF-beta signaling inhibitor, suggests that SMAD7 does not restrict the TGF-beta-mediated induction of p21, although it may prevent up-regulation of p27. cDNA oligoarray analysis indicated a pleiotropic response to methionine stress. Cell cycle and mitotic arrest is in agreement with up-regulation of NF2, ETS2, CLU, GADD45alpha, GADD45beta, and GADD45gamma and down-regulation of AURKB, TOP2A, CCNA, CCNB, PRC1, BUB1, NuSAP, IFI16, and BRCA1. Down-regulation of AREG, AGTR1, M-CSF, and EGF, IGF, and VEGF receptors and up-regulation of GNA11 and IGFBP4 signify loss of growth factor support. PIN1, FEN1, and cABL up-regulation and LMNB1, AREG, RhoB, CCNG, TYMS, F3, and MGMT down-regulation suggest that methionine stress sensitizes the tumor cells to DNA-alkylating drugs, 5-fluorouracil, and radiation. Increased sensitivity of pancreatic tumor cell lines to temozolomide is shown under methionine stress conditions and is attributed in part to diminished O(6)-methylguanine-DNA methyltransferase and possibly to inhibition of the cell cycle progression.

Alterations of tumor suppressor gene p16INK4a in pancreatic ductal carcinoma

BACKGROUND

Cell cycle inhibitor and tumor suppressor gene p16/MTS-1 has been reported to be altered in a variety of human tumors. The purpose of the study was to evaluate primary pancreatic ductal adenocarcinomas for potentially inactivating p16 alterations.

METHODS

We investigated the status of p16 gene by polymerase chain reaction (PCR), nonradioisotopic single strand conformation polymorphism (SSCP), DNA sequencing and hypermethylation analysis in 25 primary resected ductal adenocarcinomas. In addition, we investigated p16 protein expression in these cases by immunohistochemistry (IHC) using a monoclonal antibody clone (MS-887-PO).

RESULTS

Out of the 25 samples analyzed and compared to normal pancreatic control tissues, the overall frequency of p16 alterations was 80% (20/25). Aberrant promoter methylation was the most common mechanism of gene inactivation present in 52% (13/25) cases, followed by coding sequence mutations in 16% (4/25) cases and presumably homozygous deletion in 12% (3/25) cases. These genetic alterations correlated well with p16 protein expression as complete loss of p16 protein was found in 18 of 25 tumors (72%).

CONCLUSION

These findings confirm that loss of p16 function could be involved in pancreatic cancer and may explain at least in part the aggressive behaviour of this tumor type.

Smad7 abrogates transforming growth factor-beta1-mediated growth inhibition in COLO-357 cells through functional inactivation of the retinoblastoma protein

Smad7 is overexpressed in 50% of human pancreatic cancers. COLO-357 pancreatic cancer cells engineered to overexpress Smad7 are resistant to the actions of transforming growth factor-beta1 (TGF-beta1) with respect to growth inhibition and cisplatin-induced apoptosis but not with respect to modulation of gene expression. To delineate the mechanisms underlying these divergent consequences of Smad7 overexpression, we studied the effects of Smad7 on TGF-beta1-dependent signaling pathways and cell cycle regulating proteins. TGF-beta1 induced the phosphorylation of MAPK, p38 MAPK, and AKT2 irrespective of the levels of Smad7, and inhibitors of these pathways did not alter TGF-beta1 actions on cell growth. By contrast, Smad7 overexpression interfered with TGF-beta1-mediated attenuation of cyclin A and B levels, inhibition of cdc2 dephosphorylation and CDK2 inactivation, up-regulation of p27, and the maintenance of the retinoblastoma protein (RB) in a hypophosphorylated state. Smad7 also suppressed TGF-beta1-mediated inhibition of E2F activity but did not alter TGF-beta1-mediated phosphorylation of Smad2, the nuclear translocation of Smad2/3/4, or DNA binding of the Smad2/3/4 complex. Although Smad7 did not associate with the type I TGF-beta receptor (TbetaRI), SB-431542, an inhibitor of the kinase activity of this receptor, blocked TGF-beta1-mediated effects on Smad-2 phosphorylation. These findings point toward a novel paradigm whereby Smad7 acts to functionally inactivate RB and de-repress E2F without blocking the activation of TbetaRI and the nuclear translocation of Smad2/3, thereby allowing for TGF-beta1 to exert effects in a cancer cell that is resistant to TGF-beta1-mediated growth inhibition.

Adenovirus-mediated N5 gene transfer inhibits tumor growth and metastasis of human carcinoma in nude mice

The therapeutic effectiveness of cancer therapy often relies on induction of apoptotic cell death. Gene-therapy-mediated induction of apoptosis, therefore, may provide an effective means to kill cancer cells. The N5 gene encodes a death-domain-containing protein (p84N5) that can trigger atypical apoptosis from within the nucleus, suggesting it may be a candidate for use as a gene therapy for cancer. In the present study, we test the potential utility of a recombinant adenovirus designed to express the N5 gene(AdN5) for the treatment of a variety of human cancers using in vitro and animal models. In vitro, adenoviral-mediated N5 gene transfer inhibits the growth of five different tumor cell lines, but not a normal diploid fibroblast cell line. Adenoviral-mediated N5 gene transfer also reduces the growth and metastasis of primary human tumors in subcutaneous and orthotopic xenograft mouse models. Reduction in tumor cell growth in vitro and in vivo correlates with increased expression of p84N5 and induction of apoptosis. The relative sensitivity of different human cancer cells to AdN5 or Adp53 varies, suggesting that AdN5 may be effective in tumors relatively resistant to p53 gene therapy. We conclude that N5 has potential utility for the gene therapy of cancer.

Gene therapy for pancreatic cancer

Gene transfer technology has the potential to revolutionize cancer treatment. Developments in molecular biology, genetics, genomics, stem cell technology, virology, bioengineering, and immunology are accelerating the pace of innovation and movement from the laboratory bench to the clinical arena. Pancreatic adenocarcinoma, with its particularly poor prognosis and lack of effective traditional therapy for most patients, is an area where gene transfer and immunotherapy have a maximal opportunity to demonstrate efficacy. In this review, we have discussed current preclinical and clinical investigation of gene transfer technology for pancreatic cancer. We have emphasized that the many strategies under investigation for cancer gene therapy can be classified into two major categories. The first category of therapies rely on the transduction of cells other than tumor cells, or the limited transduction of tumor tissue. These therapies, which do not require efficient gene transfer, generally lead to systemic biological effects (e.g., systemic antitumor immunity, inhibition of tumor angiogenesis, etc) and therefore the effects of limited gene transfer are biologically "amplified." The second category of gene transfer strategies requires the delivery of therapeutic genetic material to all or most tumor cells. While these elegant approaches are based on state-of-the-art advances in our understanding of the molecular biology of cancer, they suffer from the current inadequacies of gene transfer technology. At least in the short term, it is very likely that success in pancreatic cancer gene therapy will involve therapies that require only the limited transduction of cells. The time-worn surgical maxim, "Do what's easy first," certainly applies here.

Molecular pathogenesis of pancreatic cancer

Our understanding of the biology of pancreatic carcinoma has greatly benefited from studies of the genetic alterations in this tumor type. The p16-CDK4-cyclinD-Rb pathway, the p53 tumor suppressor pathway, and the DPC4/Smad4 pathway are genetically inactivated in the majority of sporadic pancreatic carcinomas, whereas oncogenic K-ras signaling is almost ubiquitously activated. These genetic data have provided the basis to shape a first genetic progression model of this tumor type. Furthermore, a number of well defined genetic syndromes which are associated with an inherited risk for pancreatic carcinoma have been identified recently.

Selected features of nonendocrine pancreatic cancer

We survey some interesting features of gene expression in nonendocrine pancreatic cancer, the response to some less widely known agents as they impact on pancreatic cell proliferation and programmed death, and several developing approaches to therapy. The proliferative and cellular suicide responses of Panc-1 cells to the free radical spin trap, NTBN, and to the 5-lipoxygenease inhibitor, MK 886, the latter assessed with CLONTECH Atlas Human cDNA Array 1, are reviewed. Difficulties in identifying those factors whose suppression or augmentation could result in inhibition of malignantly transformed cell properties are considered.

Adenovirus-mediated transfer of p53 and p16(INK4a) results in pancreatic cancer regression in vitro and in vivo

Pancreatic cancer has a very poor prognosis. Current chemotherapy and radiotherapy regimens are only moderately successful. The tumour suppressor genes p53 and p16(INK4a)encode cell cycle regulatory proteins that are important candidates for gene replacement therapy. Over 80% of pancreatic adenocarcinoma cases lack detectable p16 protein while over 60% contain mutated p53 protein. We used replication-deficient recombinant adenoviruses to reintroduce wild-type p16 and p53 into pancreatic cancer cells in vitro and into subcutaneous pancreatic tumours in an animal model to determine the effect on tumour growth. Significant growth inhibition was observed in all five human pancreatic cell lines with these viruses (P < 0.002) compared with similar control viruses expressing either luciferase or beta-galactosidase. G1 arrest was observed in all cell lines 72 h after infection with Adp16. Infection with Adp53 caused significant levels of apoptosis (P < 0.004). Apoptosis was also observed to a lesser degree (P < 0.03) with the Adp16 vector. Subcutaneous pancreatic tumours, generated in nu-nu mice demonstrated significant growth suppression following injection of Adp53, Adp16 and a combination of both Adp53 and Adp16 (P < 0.0001). These results show that transfer of wild-type p53 and p16 produces significant growth suppression of pancreatic cancer in vitro and in vivo.

Gene therapy for pancreatic cancer--current and prospective strategies

Pancreatic ductal adenocarcinoma is one of the most common causes of cancer death in the developed world. Long-term survival is currently only achieved through surgical resection. Most patients have locally advanced or metastatic disease at the time of diagnosis and are therefore not amenable to resection, whilst chemotherapy and radiotherapy are by and large ineffective. Gene therapy offers an alternative to current adjuvant strategies. With approximately two-thirds of all gene therapy trials worldwide directed at cancer, the gene therapy approaches that are currently being explored for pancreatic cancer are specifically examined. Gene delivery systems, genetic targets, and combined gene delivery with chemotherapy are discussed in the context of pancreatic cancer treatment.

Novel homozygous deletions of chromosomal band 18q22 in pancreatic adenocarcinoma identified by STS marker scanning

The identification of homozygous deletions in sporadic neoplasms has been pivotal in the positional cloning of several tumor suppressor genes. Chromosomal arm 18q harbors the DPC4, SMAD2, and DCC genes and is suspected on the basis of high frequencies of allelic loss to harbor additional tumor suppressor genes. We applied high-resolution sequence-tagged site (STS) marker scanning to a panel of 106 pancreatic adenocarcinomas to identify novel regions of homozygous deletions on 18q. Three homozygous deletions were identified. Physical mapping of these deletions showed them to be nonoverlapping, but clustered in an approximately 7- to 10-Mb region of chromosome band 18q22. Each deletion spanned physical distances of nearly 1.3 to 3 Mb. A number of transcribed genes map within these deletions. The identification of these homozygous deletions might aid in the identification of novel tumor suppressor genes on chromosomal arm 18q. Genes Chromosomes Cancer 25:370-375, 1999.

The use of molecular technology in the differentiation of pancreatic cancer and chronic pancreatitis

CONCLUSION

It is concluded that currently there are limitations in the use of some of the proposed tests, whereas in the future, further progress in our understanding of the molecular biology of pancreatic disease and the development and application of existing techniques should have a greater impact on clinical practice.

BACKGROUND

Fifteen to 20% of patients with pancreatic cancer present with a resectable mass in the head of the pancreas, but there is a subgroup of patients for whom it is difficult to reach the correct diagnosis.

METHOD

This article addresses how molecular technology can be used to aid in the diagnosis of this group of patients. The clinical and scientific literature is reviewed by accessing papers through the Medline database.

RESULTS

This article reviews the limitations of conventional imaging techniques and the limitations of fine needle aspiration cytology and cytological examination of pancreatic duct secretions. The molecular biology of both pancreatic cancer and chronic pancreatitis is then reviewed with emphasis on the common molecular defects seen in these diseases. The current use of molecular techniques in the examination of cytological and histological specimens, stool, blood, and pancreatic duct secretions and how this helps discriminate between benign and malignant lesions of the pancreas is addressed. Finally, the use of novel serum screening tests in groups at high risk of pancreatic cancer is discussed.

The molecular genetics of pancreatic cancer

Pancreatic cancer is the fifth leading cause of cancer death in the United States, and despite improvements in the results of surgical treatment for this disease, little impact has been made upon overall mortality. New advances in treatment will depend upon improved adjuvant therapy, early diagnosis, and a better understanding of tumor biology. This article summarizes the results of molecular genetic studies in pancreatic cancer and their potential clinical significance. Familial predisposition to pancreatic cancer, cytogenic studies, DNA ploidy analysis, and examination of specific oncogenes and tumor suppressor genes are reviewed. The most frequent mutations detected have been in the K-ras oncogene, which occur in 80% of pancreatic cancers. These mutations do not correlate with tumor stage or survival, but can be useful in differentiating pancreatic exocrine from endocrine tumors and chronic pancreatitis. Mutations in the p53 gene occur in approximately 50% of tumors, and appear to be an independent prognostic factor for patient survival. Mutations in the CDKN2 gene are frequently seen in sporadic pancreatic cancers, and have been implicated in cases of familial pancreatic cancer. The significance of mutations in APC, MCC, DCC, c-erbB-2, RB-1, and mismatch repair genes in the genesis of pancreatic cancer is less clear.

Loss of retinoblastoma gene function and heterozygosity at the RB locus in renal cortical neoplasms

Alteration of the retinoblastoma (RB) gene, located on chromosome 13q14, has been implicated in the pathogenesis and biological behavior of several human cancers. We investigated the RB gene status by Western blotting and immunohistochemical analysis, as well as loss of heterozygosity (LOH) at the RB locus in 21 primary human renal neoplasms (including 3 oncocytomas). In only 1 of 21 tumors was there a discrepancy between Western blot and immunochemical staining. Overall, LOH was noted in 6 of 12 informative cases. However, only one of the tumors with LOH at the RB locus had loss of RB protein expression by both Western blot and immunohistochemical analysis. Loss of RB function was found in 4 of 18 carcinomas and in none of 3 oncocytomas as determined by absent RB nuclear staining in tumor cells. LOH at chromosome 13q14 was more noted in high-grade, DNA aneuploid, high-stage tumors and in patients with poor outcome. These results imply that (1) there is likely another tumor-suppressor gene on chromosome 13 involved in renal carcinogenesis, (2) LOH at chromosome 13q loci may be associated with aggressive behavior, and (3) the loss of RB function may have a role in a subset of renal carcinomas.

Molecular and immunochemical analyses of RB1 and cyclin D1 in human ductal pancreatic carcinomas and cell lines

Somatic mutations in the retinoblastoma-1 gene (RB1) and loss of RB1 protein function have been implicated in a number of human malignancies, but the role of RB1 gene and protein abnormalities in ductal pancreatic cancer (DPCA) is virtually unknown. We therefore analyzed expression of the RB1 protein immunohistochemically and/or by western blotting in a total of 54 sporadic and eight familial cases of archival and frozen DPCA and in 18 pancreatic carcinoma cell lines by using the antibodies RB-WL-1, 84-B3-1, and PMG3-245. Mutations in the RB1 promotor region and exons 13-21 of the RB1 gene were likewise examined by single-strand conformation polymorphism (SSCP) analyses and DNA sequencing of genomic DNA from 30 microdissected primary pancreatic tumors and the pancreatic carcinoma cell lines. Moreover, amplification and expression of a major regulatory component of RB1 function, cyclin D1, were assessed by southern and immunohistochemical analyses, respectively. The DPCAs were heterogeneous in both the intensity of RB1 nuclear staining and the percentage of immunoreactive cells. The tumors often had areas where RB1 staining was weak or absent adjacent to normal pancreatic tissue; however, only two of 32 archival cases and one of 30 frozen cases of DPCA completely lacked RB1 nuclear staining. Immunohistochemical and western blot analyses of 18 pancreatic carcinoma cell lines demonstrated the absence of RB1 expression in only two cell lines, Capan-1 and QGP-1. Analyses of the RB1 gene and promotor region by SSCP and DNA sequencing largely confirmed the immunochemical findings. Three of 30 primary carcinomas had abnormalities revealed by SSCP analyses. In one case a single base-pair deletion was confirmed in exon 18 and resulted in premature termination and the absence of detectable RB1 protein. A second case had TAC-->TTC missense mutation in exon 13. The third primary carcinoma could not be reliably sequenced because it had a low percentage of epithelial cells. The cyclin D1 gene was not amplified in any of the primary pancreatic tumors or cell lines examined. These immunochemical and molecular analyses of the RB1 tumor suppressor gene and cyclin D1 proto-oncogene in a large series of human pancreatic cancers and cell lines indicate that RB1 and cyclin D1 alterations occur during the development of some human DPCAs. Nevertheless, it is probable that alterations in cell-cycle regulation in DPCAs more frequently involve pathways other than those involving RB1 and cyclin D1.