Catherine, Princess of Wales, announced in a video released Friday by Kensington Palace that cancer was found following her abdominal surgery in January. The former Kate Middleton, 42, is receiving preventive chemotherapy, medically known as adjuvant chemotherapy, to destroy any cancer cells still lurking in her body.

“The surgery was successful,” she said. “However, 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’m now in the early stages of that treatment.”

According to The Sunday Times, preventive chemotherapy is usually given after patients have had surgery to remove tumors, and typically involves several doses of chemotherapy drugs over at least three months. Dr. Ben Ho Park, director of Precision Oncology at Vanderbilt School of Medicine tells TODAY.com that the most common types of cancer that are found after abdominal surgery are gastrointestinal, urinary and genital.

But he added that it “could be anything” given the information that is currently available. He explained that preventive chemotherapy is conducted after initial treatment like surgery to help prevent cancer from recurring. Treatment options are based on the stage of cancer, the type of cancer and even the age of the patient, Park said.

“Even though the surgeons removed everything they can see, there could be cancer cells floating around in the body that, if left untreated, may come back later,” he added, and may then be uncurable. Clinical trials have shown that chemotherapy after initial treatment for some cancers can reduce the risk of the cancer coming back.

According to TIME, this treatment usually involves the same chemotherapy drugs that people receive to treat active or advanced cancer. Adjuvant chemotherapy is meant to kill any remaining, microscopic cancer cells a surgeon could not see and may have missed, and to destroy any cells that may have escaped and spread to other parts of the body.

Depending on the type of cancer, studies have shown that giving “anywhere from three to six months of chemotherapy after surgery can significantly reduce the risk of cancer coming back,” said Dr. Jeremy Jones, a medical oncologist at the Mayo Clinic. “It’s standard care to reduce the risk of recurrence for many types of cancer.”

Park added that there is a lot of uncertainty with preventive chemotherapy. Even after treatment, patients, and their doctors “will still not know” if the cancer will recur.