What is preventative chemotherapy? Here's Kate Middleton's cancer ...

Princess Kate has revealed why she has been out of the public eye for months — she has been diagnosed with cancer following major abdominal surgery. 

The Princess of Wales did not give details of the type or stage of the cancer, or share her specific treatment plan.

But she did say she was receiving "preventative chemotherapy" in a personal video message.

Here's what we know about preventative chemotherapy.

What is preventative chemotherapy?

Preventative chemotherapy is given before or after a primary treatment, such as surgery, to reduce the chance of a cancer returning or spreading.

Preventative treatments given before the primary treatment are called neoadjuvant therapy.

Preventative treatments given afterward, as in Princess Kate's case, are called adjuvant therapy.

Adjuvant chemotherapy can "mop up" any remaining cancer cells, but its value varies by cancer type and by its size and location, said Professor Bob Phillips, a paediatric oncologist at the University of York.

Later, patients may go on to receive maintenance therapy to prevent the cancer's return or to delay its growth.

What does treatment look like?

Treatment can span from a few months to more than a year.

Oncologists today view cancer as an array of diseases, each of which requires its own specific treatment plan with a range of therapies, including intravenous infusions, pills, or radiation.

"There are a very large number of chemotherapy drugs and combinations resulting in many different regimens, even for a single type of cancer," said Mangesh Thorat, a breast surgeon at Homerton University Hospital.

Dr Phillips said patients received "four to six cycles, each lasting 21 days and consisting of a day or few days of chemo, then time for the body to recover from it".

In other cases, chemotherapy is administered daily, or every two or four weeks, he noted.

What are the side effects of chemotherapy?

According to the Cancer Council, possible side effects from chemotherapy include:

FatigueNausea or vomitingConstipationHair lossMouth soresThinking and memory changesChanges in hearingNumbness in your hands or feet

Moffitt Cancer Centre gynecological oncologist Monica Avila said there were medications that could improve these side effects.

"A patient can take anywhere from a few weeks to a month or two to recover from those effects," Dr Avila said.

She also said cold caps that cool the scalp could help prevent hair loss.

How long does it take to recover from chemotherapy?

Recovery times vary widely, but even when treatment comes to an end, it can take months for a patient to resume full activity.

Catherine will not return to royal duties until she has been cleared by her medical team, but is expected to attend some events when she is feeling well.

The palace said this would not be considered a return to public life, but would allow Catherine to be present in moments that matter to her.

They also said she was on a recovery pathway.

What type of cancer does Princess Kate have?

We don't know the type of cancer the princess has.

And Kensington Palace said that no other details would be provided about her cancer or her treatment, other than she started it in late February.

Reuters/AP/ABC