A review of over 140 scientific studies on colorectal cancer may point to a more effective way of diagnosing and preventing this deadly disease.
The conventional view is that an altered gene signal that instructs cells to grow is the cause of colorectal cancer. McGill University Health Centre (MUHC) pathologist, Dr. Jeremy Jass, will publish a study in the September issue of Gastroenterology, which suggests that the disease is caused by the failure of a signal that normally tells cells to die.
"The difference between these two mechanisms for causing increased cell numbers may appear subtle, but our research presents a totally new model for explaining the evolution of colorectal cancer," says Jass. "The type of polyp - a small growth in the lining of the colon - that results when a cell refuses to die has been regarded as completely innocent up till now. However, when a cell ignores the signals to die it can continue to grow even when it loses the ability to repair its own damaged DNA.
The silencing of the gene that controls cell death is due to a chemical change to DNA called methylation. The same mechanism silences the genes that control the repair of DNA damage. DNA methylation is different from a mutation, or change in the structure of a gene, as it is potentially reversible. However, once cells lose the ability to repair DNA, permanent genetic mutations occur and the progression to cancer is then rapid.
Jass's conclusion from these studies is that a decrease in programmed cell death is likely to be the first event that drives a cell towards cancer. "This study is important because it will radically alter our thinking about how to prevent, manage and diagnose the disease," says Jass.
"Our hope is to use this model to develop better screening programs to more accurately identify patients who are at risk of developing colorectal cancer," he added
Colon and rectal cancers, referred to as colorectal cancer, are life-threatening tumors that develop in the large intestine. The Canadian Cancer Statistics estimates that 17 200 people will be diagnosed with the disease this year. Only lung cancer is responsible for more cancer deaths.
"Our research underscores the importance of regular screening tests for everyone over 50 years of age and those who have been identified as being at risk. Colorectal cancer is almost always a preventable disease when proper screening is used," says Jass.