Julinor Bacani, M.D., Ph.D.
Ph.D. Candidate, Laboratory Medicine and Pathobiology, University of Toronto
Anatomical Pathology Resident, University of British Columbia
Samuel Lunenfeld Research Institute - Mount Sinai Hospital
600 University Avenue, Room 989
Toronto, Ontario Canada M5G 1X5

Frequency of E-cadherin (cdh1) and mismatch repair (MMR) germline mutations in young gastric cancers

Gastric carcinoma (GC) is a major cause of cancer death in Canada due to its late stage at presentation. Improvements in early detection, diagnosis and treatment of GC are needed. Currently, a multi-factorial model is accepted with hereditary and environmental factors playing various roles. However, the relative contributions of these factors remain unclear. Furthermore, GC is heterogeneous and classification needs to better reflect molecular alterations and patient outcomes.

The main objectives of this study are: 1) to characterize important genetic factors in a well-defined population-based cohort of young GC and 2) to determine whether molecular profiling can improve GC classification and prognostication. The frequencies of germline mutations in CDH1/E-cadherin and mismatch repair/MMR genes in the population are not known.  CDH1 germline mutations are important in hereditary diffuse GC families and will be estimated by single strand conformation polymorphism and sequencing. Germline mutations in MMR genes characterize hereditary nonpolyposis colon cancer syndrome leading to microsatellite instability/MSI in young colon cancer and young GC patients.

Potential mechanisms involved in the MSI positive cases will be investigated using immunohistochemistry for known MMR proteins, methylation-specific PCR for epigenetic silencing, and mutational analyses for genetic inactivation. Finally, high-throughput tissue microarrays will be used to examine the potential of immunohistochemical markers in GC classification and prognostication.

By studying important genetic factors, we will ascertain not only their relative contribution but also their putative interactions in GC. The data derived from this population-based study, may be useful in developing more effective 1) policies to detect and screen patients at higher risk of GC and 2) treatments that tailor to specific molecular alterations in GC.

Marina Croitoru BSc.
MSc. Candidate, Institute of Medical Science, University of Toronto
Samuel Lunenfeld Research Institute-Mount Sinai Hospital
600 University Avenue, Room 989
Toronto, Ontario Canada M5G 1X5

Germline MYH Mutations and Risk of Colorectal Cancer

Colorectal cancer is one of the most common cancers in North America.  The majority of tumors develop through a stepwise progression from normal epithelium to adenoma and ultimately invasive carcinoma.

The MYH gene codes for an enzyme, which is part of the base excision repair (BER) system, responsible for protecting cells from damage caused by endogenous or exogenous oxidative processes. Recent studies have shown that biallelic germline MYH mutations are associated with an increased risk of developing colorectal adenomas and cancer, as an autosomal recessive disease. 

Using the resources of the Ontario Familial Colorectal Cancer Registry (OFCCR), we are conducting the largest North American population-based case-control study to determine the association between carrying biallelic and monoallelic germline MYH mutations, and the risk of developing colorectal cancer. We are also examining the role of germline MYH mutations in two clinic-based registries of multiple adenomas patients from Toronto and Newfoundland. 

The elucidation of the pattern of disease associated with carrying MYH mutations will clarify a fraction of hereditary colorectal cancer cases.  The results of these studies will lead to improved screening practices (genetic testing and colonoscopy) for those individuals at high risk.

Lynn Mikula
Supervisor:  Dr. Steven Gallinger
Department of General Surgery, University of Toronto
Samuel Lunenfeld Research Institute - Mount Sinai Hospital
600 University Avenue, Room 989
Toronto, Ontario Canada M5G 1X5

Functional genetic analysis of a putative tumour suppressor involved in pancreatic adenocarcinoma.

Pancreatic adenocarcinoma is the fifth leading cause of cancer death in North America.  The mortality of the disease approximately equals its incidence year after year, and therapeutic options are limited by low resection rates and high chemoresistance.  The environmental and genetic factors contributing to the disease remain poorly understood. 

We have identified a balanced germline translocation in an individual with early-onset pancreatic cancer.  Analysis of this region has identified a novel gene (Translocated in Pancreas Cancer, TPC) with a high degree of inter-species homology.  TPC is expressed in a wide variety of human tissues, including pancreas and colon.  Gene expression data and loss of heterozygosity analyses suggest that TPC may be a tumour suppressor gene involved in both pancreatic and colorectal cancers. 

Current work is focused on functional genetic analysis of TPC.  Several cancer cell lines have been stably transfected with TPC and these will be used to undertake phenotypic assays.  These stable transfectants will also be injected into SCID or nude mice to characterize their tumorigenicity. 

Furthermore, mammalian gene silencing of TPC will be carried out using RNA interference.  RNAi will initially be performed on colon and pancreas cancer cell lines that highly express TPC, and ultimately on embryonic stem cells.  The eventual goal is to create a knock-down mouse using RNAi.  We hope to demonstrate that TPC is a novel tumour suppressor gene involved in the carcinogenesis of pancreatic and other gastrointestinal malignancies.

George Zogopoulos, M.D., Ph.D.
Postdoctoral Research Fellow, Samuel Lunenfeld Research Institute
General Surgery Resident, University of Toronto
Mount Sinai Hospital
600 University Avenue, Room 989
Toronto, Ontario Canada M5G 1X5

FUNCTIONAL CHARACTERIZATION OF A NOVEL CANDIDATE TUMOR SUPPRESSOR GENE

Pancreatic ductal adenocarcinoma is a lethal human malignancy. The molecular mechanisms leading to its development and progression remain poorly understood.

Our laboratory has recently identified a balanced germline translocation in a young pancreatic cancer patient resulting in disruption of a novel gene (Translocated in Pancreatic Cancer). Loss of heterozygosity and gene expression data suggest that TPC is a tumor suppressor gene.

We are currently screening pancreatic and colorectal carcinomas for germline and somatic TPC gene mutations. In addition, given the presence of a putative CpG island in the TPC gene promoter region, these tumors are also being examined for TPC gene silencing by hypermethylation.

Our series of tumors is being further evaluated for loss of TPC mRNA and protein expression in tumor vs. normal epithelium using immunohistochemical and in situ hybridization approaches.

To study TPC function in vivo, we are employing RNA interfering knockdown methodology to create a transgenic mouse model lacking TPC expression. The goal of these investigations is to determine whether TPC is a tumor suppressor gene with a role in pancreatic cancer and other gastrointestinal malignancies.