What is cancer and how does it start?

Put simply, cancer involves the uncontrolled growth of cells in the body. While there are a number of possible causes, they are all related to errors that happen in the cell’s genetic instructions, or DNA.

The cell can make a random mistake when replicating, resulting in a cell that grows faster than other cells around it. Or, the cell can be damaged by carcinogens, such as ultraviolet light or the chemicals in cigarettes.

Some cancers can also occur when a cell’s “self-destruct” code malfunctions. Our bodies recognise when cells are damaged, grow too rapidly or otherwise behave abnormally, then react by sending out chemical signals that tell the cells to stop growing or self-destruct. Errors can alter that signal or affect a cell’s ability to recognise it; the cell turns a deaf ear to the instructions from the body to cease and desist.

Most genetic errors that cause uncontrolled cell growth occur because of bad luck. The longer we live, the more of our cells divide, increasing the statistical likelihood that one of those cells will make a mistake when replicating and develop into cancer. This is why most cancers are diagnosed in older adults.

Another form of bad luck includes genetic mutations we’re born with. It is estimated that up to 10% of cancers are caused by inherited genetic abnormalities such as BRCA1 and BRCA2, which are linked to breast, ovarian and prostate cancers, among others.

Some genetic errors are introduced by viruses. Anywhere from 13 to 20% of cancers worldwide are thought to be due to viruses, such as human papilloma virus, or HPV, Epstein-Barr virus and hepatitis B and C, and bacteria, such as Helicobacter pylori.

Other extrinsic or “outside of the body” factors can break or damage a cell’s DNA and lead to cancer, including smoking, alcohol intake and exposure to ultraviolet radiation from the sun or other sources, such as tanning beds. Less common DNA-damaging culprits include environmental exposures such as industrial chemicals, nuclear radiation, chemotherapy or radiation therapy used to treat other cancers.

Once created, cancer cells are insidious: they can instruct blood vessels to grow toward tumours, thus ensuring their own survival by having an adequate supply of oxygen and nutrients; they can hide from the immune system, cloaking themselves to prevent their own destruction; and they can even trick the immune system into helping them survive and thrive.

Why have cancer rates increased over time?

Overall, people are living longer because deaths from cardiovascular disease, stroke and other medical conditions have declined. As we extend our lifespan, though, we increase that statistical likelihood that our cells accumulate genetic mutations.

Cancer rates can also change depending on how we define “cancer”. For example, many of my patients have a type of bone marrow cancer called myelodysplastic syndromes. It was only about 25 years ago that the US Centers for Disease Control and Prevention and the National Cancer Institute formally recognised this condition as a cancer, and started tracking it alongside more common cancers like those of the lung, breast or prostate. Once these government agencies decided to call myelodysplastic syndromes a cancer, overnight the numbers of cancers diagnosed in the US increased by about 20,000 per year.

And much of the increase in cancer diagnoses can be attributed to better detection. Radiology scans have become more refined and sensitive, making them better at detecting abnormalities that lead to cancer diagnoses. Laboratory tests have been developed to identify markers in the blood (such as certain proteins) that suggest cancer may be present before it otherwise would have been discovered.

Cancer screening programmes, which are designed to detect cancer in its early stages, when it is potentially more curable, have uncovered more slower-growing cancers – including ductal carcinoma in situ of the breast in women or early stage prostate cancer in men – that previously never would have been diagnosed.

While there are increases in certain kinds of cancer (which generate a lot of discussion), such as colorectal cancer in people under 50, it’s also true that cancer rates are dropping in other groups, like colorectal cancer in people over 50.

Treatments to target and eliminate cancer keep getting better

There is some good news: people are living longer than ever following a cancer diagnosis. The National Cancer Institute’s Division of Cancer Control & Population Sciences estimates that there are over 18 million cancer survivors in the US and that this number is expected to grow to 26 million by 2040. Seventy per cent of survivors live five or more years following their diagnosis, approximately half live 10 or more years and three-quarters of survivors are 60 years or older.

While some of the improved survival from cancer can be attributed to the increased number of early-stage cancers detected, we can also thank advancements in cancer therapies. Traditional chemotherapies damage cells during the division process, taking advantage of those rapidly dividing cancer cells. Other drugs, called angiogenesis inhibitors, help prevent the growth of blood vessels that feed the tumour. These treatment approaches, though, are not always specific to a given person’s cancer, and tend to affect the growth of noncancerous cells, too.

But over the past two to three decades, medications have been developed that target specific genetic mutations within the cancer cells, such as the HER2 abnormality in breast cancer, ALK in lung cancer, FLT3 in leukaemia and more recently KRAS in pancreatic cancer, among many, many others.

And within the past 10 to 15 years, there has been a revolution in the use of immunotherapy to treat cancer, with drugs that specifically target proteins on the outside of cancer cells, or that harness a patient’s own immune system to essentially train it to find and eliminate cancer. These newer, innovative treatments have improved the rates and duration of remission and even survival for a number of cancers, and have retooled how we treat cancer.

So while it is true that there seems to be more cancer than ever, there is also more hope than ever, as cancer is being detected earlier, eliminated more effectively or transformed to a chronic condition rather than a life-threatening one.