Catherine, Princess of Wales, is undergoing treatment for cancer. In a video thanking followers for their messages of support after her major abdominal surgery, the Princess of Wales explained, “tests after the operation found cancer had been present.”

“My medical team therefore advised that I should undergo a course of preventative chemotherapy and I am now in the early stages of that treatment,” she said in the two-minute video.

No further details have been released about the Princess of Wales’ treatment.

But many have been asking what preventive chemotherapy is and how effective it can be. Here’s what we know about this type of treatment.

It’s not the same as preventing cancer

To prevent cancer developing, lifestyle changes such as diet, exercise and sun protection are recommended.

Tamoxifen, a hormone therapy drug can be used to reduce the risk of cancer for some patients at high risk of breast cancer.

Aspirin can also be used for those at high risk of bowel and other cancers.

How can chemotherapy be used as preventive therapy?

In terms of treating cancer, prevention refers to giving chemotherapy after the cancer has been removed, to prevent the cancer from returning.

If a cancer is localised (limited to a certain part of the body) with no evidence on scans of it spreading to distant sites, local treatments such as surgery or radiotherapy can remove all of the cancer.

If, however, cancer is first detected after it has spread to distant parts of the body at diagnosis, clinicians use treatments such as chemotherapy (anti-cancer drugs), hormones or immunotherapy, which circulate around the body .

The other use for chemotherapy is to add it before or after surgery or radiotherapy, to prevent the primary cancer coming back. The surgery may have cured the cancer. However, in some cases, undetectable microscopic cells may have spread into the bloodstream to distant sites. This will result in the cancer returning, months or years later.

With some cancers, treatment with chemotherapy, given before or after the local surgery or radiotherapy, can kill those cells and prevent the cancer coming back.

If we can’t see these cells, how do we know that giving additional chemotherapy to prevent recurrence is effective? We’ve learnt this from clinical trials. Researchers have compared patients who had surgery only with those whose surgery was followed by additional (or often called adjuvant) chemotherapy. The additional therapy resulted in patients not relapsing and surviving longer.

How effective is preventive therapy?

The effectiveness of preventive therapy depends on the type of cancer and the type of chemotherapy.

Let’s consider the common example of bowel cancer, which is at high risk of returning after surgery because of its size or spread to local lymph glands. The first chemotherapy tested improved survival by 15%. With more intense chemotherapy, the chance of surviving six years is approaching 80%.

Preventive chemotherapy is usually given for three to six months.

How does chemotherapy work?

Many of the chemotherapy drugs stop cancer cells dividing by disrupting the DNA (genetic material) in the centre of the cells. To improve efficacy, drugs which work at different sites in the cell are given in combinations.

Chemotherapy is not selective for cancer cells. It kills any dividing cells.

But cancers consist of a higher proportion of dividing cells than the normal body cells. A greater proportion of the cancer is killed with each course of chemotherapy.

Normal cells can recover between courses, which are usually given three to four weeks apart.

What are the side effects?

The side effects of chemotherapy are usually reversible and are seen in parts of the body where there is normally a high turnover of cells.

The production of blood cells, for example, is temporarily disrupted. When your white blood cell count is low, there is an increased risk of infection.

Cell death in the lining of the gut leads to mouth ulcers, nausea and vomiting and bowel disturbance.

Certain drugs sometimes given during chemotherapy can attack other organs, such as causing numbness in the hands and feet.

There are also generalised symptoms such as fatigue.

Given that preventive chemotherapy given after surgery starts when there is no evidence of any cancer remaining after local surgery, patients can usually resume normal activities within weeks of completing the courses of chemotherapy.

Ian Olver, Adjunct Professsor, School of Psychology, Faculty of Health and Medical Sciences, University of Adelaide

This article is republished from The Conversation under a Creative Commons license. Read the original article.