Cancer is now the second leading cause of death in Canada and its incidence is expected to increase by 70% by the year 2015. The good news is that with improved screening tests, availability of comprehensive information, and better treatment, more than half of all people with cancer will survive the disease, and many go on to live happy and productive lives.

More than one disease

Cancer is not a single disease but a label used for well over 100 - and possibly as many as 200 - different diseases. Each of these diseases involves the uncontrolled growth of abnormal cells. Normally, cells divide and produce new cells in an organized fashion when the body needs them to maintain healthy body functions or to repair injured tissue.

When this normal function stops working, cells reproduce even when the body doesn't need these new cells. This creates a mass of cells called a tumour. A tumour can be benign, which means non-cancerous, or it can be malignant, which means cancerous. Cells can break away from a malignant tumour and enter the blood stream or the body's lymph system, spreading to and damaging other healthy body tissues and organs.

Primary and secondary cancers

Cancers are typically named after the part of the body where they begin. For example, breast cancer starts in the breast and prostate cancer begins in the prostate. These original cancer growths are called primary tumours. If the cancer spreads, or metastasizes, to a new site, that new tumour is called a secondary tumour.

Each type of primary tumour has its own way of spreading. For example, colon cancer typically targets the liver or sometimes the lungs. Prostate cancer often invades the bone. It's this capacity of malignant tumours to spread and invade tissue that makes them particularly life-threatening.

Why cancers develop

Nobody knows exactly why these cells divide and grow uncontrollably. Over the years, scientists have made huge leaps forward in understanding how cancers grow. But there's still a lot to learn.

What we do know is that cancer is caused by a complex mix of heredity, lifestyle factors, and cancer-causing substances in the environment called carcinogens.

Inherited genes

You are born with thousands of genes in each cell of your body. These genes are made up of DNA, the blueprint for all body functions. Genes are switched on and off by certain signals, starting from either inside the body or externally.

One internal signal that might set a tumour in motion comes from what's called a cancer gene. If you're born with such a gene, you may be more likely to develop cancer than someone who doesn't have this gene. Only an estimated 5-10% of cancers, are caused by an inherited gene. This means that even if you have a strong family history of cancer, you won't necessarily develop it. Other factors must be at work too.

Lifestyle factors

A more important signal affecting the genes probably comes from lifestyle factors, such as tobacco use, an unhealthy diet, physical inactivity, or exposure to sunlight or other environmental factors. Together, these lifestyle factors account for at least 50% of all cancers. These external elements may damage the DNA and cause genes to mutate or change. Normally, your body has a repair mechanism that "fixes" this damaged DNA. But when this repair mechanism breaks down, cancer cells continue to multiply, leading to a cancerous tumour. It can take many years for the cancer to become large enough to be detected.

Reducing your risk

Your best protection against cancer is to minimize these external factors. This means eating a healthy diet that includes plenty of vegetables and fruits, maintaining a healthy body weight, getting regular physical activity, and avoiding direct sunlight. And, of course, it means refraining from smoking and avoiding second-hand smoke.

Your next best protection is finding the cancer early when it is most treatable. In most cases, the earlier a cancer is detected and treated the better your chances for long-term survival. It's also important to tell your doctor or dentist about any changes in your health.