Although it is not known what type of cancer Princess Catherine has, oncologists say that what she described in her public statement that was released on Friday — discovering a cancer during another procedure, in this case a “major abdominal surgery” — is all too common.

“Unfortunately, so much of the cancer we diagnose is unexpected,” said Dr. Elena Ratner, a gynecologic oncologist at Yale Cancer Center who has diagnosed many patients with ovarian cancer, uterine cancer and cancers of the lining of the uterus.

Without speculating on Catherine’s procedure, Dr. Ratner described situations where women will go in for surgery for endometriosis, a condition in which tissue similar to the lining of the uterus is found elsewhere in the abdomen. Often, Dr. Ratner says, the assumption is that the endometriosis has appeared on an ovary and caused a benign ovarian cyst. But one to two weeks later, when the supposedly benign tissue has been studied, pathologists report that they found cancer.

In the statement, Princess Catherine said she was is getting “a course of preventive chemotherapy.”

That, too, is common. In medical settings it is usually called adjuvant chemotherapy.

Dr. Eric Winer, director of the Yale Cancer Center, said that with adjuvant chemotherapy, “the hope is that this will prevent further problems,” and avoid a recurrence of the cancer.

It also means that “you removed everything” that was visible with surgery, said Dr. Michael Birrer, director of the Winthrop P. Rockefeller Cancer Institute at the University of Arkansas for Medical Sciences. “You can’t see the cancer,” he added because microscopic cancer cells may be left behind. The chemotherapy is a way to attack microscopic disease, he explained.

Other parts of Catherine’s statement also hit home for Dr. Ratner, particularly her concern for her family.

“William and I have been doing everything we can to process and manage this privately for the sake of our young family,” the statement said.

And, “it has taken us time to explain everything to George, Charlotte, and Louis in a way that is appropriate for them, and to reassure them that I will be okay.”

Those are sentiments that Dr. Ratner hears on a regular basis and reveal, she says, “how hard it is for women to be diagnosed with cancer.”

“I see this day in and day out,” she said. “Women always say, ‘Will I be there for my kids? What will happen with my kids?’”

“They don’t say, ‘What will happen to me?’”