‘Overdiagnosis’: some breast cancer treatments may have been unnecessary, study suggests

When Jenny* had a mastectomy after being diagnosed with breast cancer, she believed the major surgery to remove her breast, although traumatic, had saved her life.

She described feeling "rage" when at a follow-up appointment three years later, she said to her surgeon, "I would probably be dead by now" if she had not received the surgery, to which he replied: "Probably not."

It was only then, after she had already undergone invasive and life-changing treatment, that Jenny learned about "overdiagnosis".

While breast cancer screening programs are essential and save lives, sometimes they also detect lumps that may never go on to cause harm in a woman's lifetime, leading to overtreatment, and psychological and financial suffering.

Jenny is one of 12 women from the UK, US, Canada and Australia whose stories were published in the medical journal BMJ Open on Thursday. It is the first study to interview breast cancer patients who believe they may have received unnecessary and harmful treatment, highlighting the effect this has had on their lives.

"The usual story of breast cancer screening is 'screening saves lives'," an author of the study and a professor of public health at the University of Sydney in Australia, Alexandra Barratt, said.

"This study reports the other side of the story - how breast cancer screening can cause harm through overdiagnosis and overtreatment."

In Jenny's case, she learned from her surgeon only after her mastectomy that her cancer may not ever have progressed to cause harm or symptoms, and that ongoing monitoring or less invasive treatments may have been an option.

Overdiagnosis occurs when cancers are correctly diagnosed, but at such an early stage that those cancers are unlikely to ever go on to grow or spread in a person's lifetime, and are not causing any symptoms. Due to improved medical technology, these are being detected more often.

This early diagnosis can sometimes be useful for ongoing monitoring. But sometimes as a result of the cancer being identified, psychological distress occurs, and treatment is nonetheless recommended by a specialist or preferred by the patient, including treatments that carry risks and can be invasive. This is known as overtreatment.

Prostate cancer is another example where overdiagnosis and overtreatment is an established issue. However, there are some cancers, such as ovarian cancer, for which the prognosis can be dire by the time it is diagnosed, and for which early detection is crucial. Early detection and treatment of ovarian cancer is rare because it is a cancer that can quickly dislodge from the fallopian tube or ovary surface and spread, making it much harder to treat and highly fatal.

Estimates of breast cancer overdiagnosis vary from 10% to 30%, depending on the study methods. A Cochrane review of screening mammography found that "for every 2,000 women invited for screening throughout 10 years, one will have her life prolonged".

"In addition, 10 healthy women, who would not have been diagnosed if there had not been screening, will be diagnosed as breast cancer patients and will be treated unnecessarily."

Prof Chris Pyke, vice president of the Royal Australasian College of Surgeons and a past president of Breast Surgeons of Australia and New Zealand, said the paper from Barratt and her colleagues should be "congratulated".

"We must all get used to the idea that every time you have a screening program for any disease at all, there will be a certain number of people diagnosed with diseases that would never have affected the person," Pyke said. "I think it's good to get the issue out there in the open for discussion."

He said surgeons do receive ongoing training about screening, risks and benefits, and how to communicate those well. "Whether that means every single breast cancer surgeon in Australia has overdiagnosis at the forefront of their mind during advice they give is another matter."

An independent UK review into the issue concluded that for every 10,000 women invited to screening from age 50, about 681 cancers will be found, of which 129 will represent overdiagnosis, and 43 deaths from breast cancer will be prevented. They estimated that in the UK, about 3,000 women are overdiagnosed with breast cancer every year, and about 1,000 deaths are prevented.

"As a result of the review, for the last 10 years women in the UK have been receiving information about the benefits of screening as well as the harms of overdiagnosis," Barratt said. "We believe that policy should also be implemented in Australia and other countries with screening programs."

Kirsten Pilatti, the chief executive of the Breast Cancer Network Australia, said the challenge is many women will never know for sure if they were overdiagnosed, and "we need to be very careful about the message we send to the public when talking about overdiagnosis". The earlier a cancer is found, the better the chances of surviving it, she said, with screening programs a part of the reason survival rates from breast cancer have improved significantly.

"We have also seen a reduction in breast cancer screening during the pandemic and as a result we are concerned about how that, combined with ongoing pressures on health systems, might translate into later detection and treatment, and poorer outcomes for women," Pilatti said.

"But we do need to move to a risk stratification model where we use the latest in research to identify those women at greater risk from breast cancer and tailor screening for them."

Major cancer organisations worldwide now acknowledge the risks of overdiagnosis and have called for patients to be given greater information about the risks and harms of screening and treatment for a variety of cancers.

Dr Anna Samecki, a general practitioner and medical adviser at NPS MedicineWise, said while the BMJ Open study interviewed a small number of women, it is nonetheless an "informative qualitative study" that highlighted a "small but real" risk of overdiagnosis.

"The study highlights the importance of informed consent and the need to inform patients about the risks of proposed procedures," she said.

"The study found that women who became aware of overdiagnosis following breast cancer screening experienced negative psychosocial consequences including feelings of anger, remorse, and loneliness."

Sally*, an Australian woman who participated in the study, told the Guardian that when she was diagnosed with ductal carcinoma in situ, considered the earliest stage of breast cancer and non-invasive at this stage, her surgeon told her she would need a mastectomy. Sally had no symptoms.

The surgeon that she went to for a second opinion also only offered mastectomy, but she contacted a third surgeon who advised a mastectomy but was willing to perform a lumpectomy, a less invasive procedure where the cancer and tissue that surrounds it is removed. Eight years after the lumpectomy, Sally is still healthy and cancer-free. She firmly believes a mastectomy would have been overtreatment and is relieved she did not undergo the procedure.

She said it was "incredibly difficult" to have a conversation about treatment with clinicians, one who asked what "nonsense" she had been reading because she had decided not to have a mastectomy.

She said she understands why surgeons recommend mastectomy. "Cancer surgeons often see extremely sick people and they want to do all they can to prevent that," she said.

"There is sometimes more ambiguity to deal with when other treatment options are recommended. There is that chance it may come back or get worse. But I would like more doctors to be willing to at least have the conversation with their patients."

*Names changed to protect identity