Cancer immunotherapy – redefining vaccines

Box 2 | What is cancer?

One in two men and one in three women are diagnosed with cancer by the time they turn 85. In Australia, more than 39,000 people die from cancer every year. We've all heard of cancer, we regularly hear statistics on different types of cancer, but how many of us really understand what it is? For starters, it's not just one disease; there is a range of types of cancer with a range of causes.

One common theme though, is that cancer cells develop from normal body cells that have become out of control. They don't respond normally to signals that control cell growth and death, and instruct cells to do specialised jobs. As a consequence, cancer cells divide more often than the normal body cells they came from, and die less often than new cells are made. This produces a growth or tumour. If tumour cells stay put, the tumour is described as benign, but if they also develop the ability to spread and invade other tissues in the body, a process called metastasis, the tumour becomes malignant, or a cancer.

What causes cancer cells to be out of control? The simple answer is damage to the cell's programming, held in the genes. There must be several changes to a cell's genes before they become able to make a tumour, and several more before the tumour becomes invasive. These changes can be caused by a range of factors, including exposure to UV light, X-rays, chemicals or viruses. Also, some people inherit gene variants that predispose them to particular cancers, which is why some cancers run in families.

The genetic changes which promote cancer commonly occur in genes that control normal cell growth and death. Two types of gene commonly damaged in cancer, are proto-oncogenes and tumour suppressor genes. These genes are often likened to the accelerator and brake in a car. Proto-oncogenes speed up cell growth when needed and tumour suppressor genes slow it down. But when either of these genes is changed, cell division can get out of control. For example, p53, also known as the 'guardian of the genome', acts as a tumour suppressor gene (the brakes of the cell). Scientists have found that p53 no longer functions properly (is mutated) in 40 per cent of all cancers.

DNA repair genes belong to another group of genes often damaged in cancer cells. These are like the mechanics of the cell, they look after the DNA, making repairs when it is damaged. If the repair genes mutate they may no longer be able to fix other cancer-causing mutations.

Box
Box 1. Guarding against viral cancer – Gardasil®

Related sites
Understanding cancer (National Cancer Institute, USA)
Cell biology and cancer (Learner.org, USA)
DNA and genes (Back to basics, Australian Academy of Science)
Cancer, genes and inherited predisposition overview (Centre for Genetics Education, NSW Government)

External sites are not endorsed by the Australian Academy of Science.
Posted September 2008.