Doctors face particular challenges when they become patients—challenges that they are rarely prepared for. It is hard to relinquish control and allow others to dictate the treatments that you yourself are used to doling out. It is crushing to know your own prognosis in the starkest terms—a 65 percent chance of surviving for 10 years, in O’Riordan’s case. It is awkward to see your own former patients while you’re being treated: To strike up a chat would break confidentiality.

And it is difficult to be cut off from the same supportive forums and networks that other patients use to share experiences and support; if you let slip that you’re a doctor, you become a source of information, rather than a comrade in illness. After getting her diagnosis, O’Riordan tweeted about it, and began blogging about her experiences. She was contacted privately by several people who said: I’m a doctor, and no one knows I have cancer. She ended up with a secret network of 15 such people. Two of them have since died.

After a nine-month-long triathlon of surgery, chemotherapy, and radiotherapy, O’Riordan got the all clear. The cancer was gone. She spent the better part of a year building back her energy levels, getting counseling, wrangling with hospital bureaucracy, and writing a book with another doctor-turned-patient. In April 2017, she returned to her hospital and worked part-time. At the end of the year, she started operating again.

O’Riordan still has some physical problems. Chemotherapy can famously fog the brain for years after the treatments end, so she still finds it hard to concentrate for more than half a day. When she returned to the operating room, she performed all the old procedures flawlessly, but at one point, she forgot the names of her instruments. “I was closing the skin and needed forceps to hold the tissue, but I couldn’t remember what they were called,” she says. “I was doing the action with my hand, and thankfully, with a good scrub nurse, you don’t need to ask.”

The emotional challenges are tougher. On her first day back, O’Riordan attended a multidisciplinary team meeting, where doctors of different specialties gather to plan a patient’s care. “The first patient was a woman of my age and with my details, and I heard them all say: That’s a really bad prognosis,” she recalls. “That was really hard.” She kept seeing herself reflected in the patients. She saw a woman burst into tears at her diagnosis, and suddenly, she was reliving her own treatment. She saw a patient being told that their cancer had returned, and she wondered if she was looking at her future. Her experiences on both sides of the doctor-patient divide repeatedly rose to the surface and collided.

How much, for example, should she share with her own patients? O’Riordan had blogged regularly about her cancer. She had even done a TEDx talk. But she practices medicine under her maiden name, so few people would make the connection between her online persona and her professional one. Ultimately, she decided to say nothing at first, revealing her experiences only to patients who have completed their treatments and are dealing with the side effects. It helps them, she says, to know that their doctor fully understands how hard it is to live with breast cancer. “You don’t want to compare yourself to other people,” she says. “But when they’re going through that journey, it helps to know that the doctor has, too.”