Cancer screening a shared decision

SHARED decision making between doctors and patients is the best approach to deciding if the benefits of undergoing cancer screening outweigh the risks of overdiagnosis for any particular patient, says a leading public health expert.

Professor Chris Del Mar, professor of public health at Bond University and a member of the Royal Australian College of General Practitioner’s Red Book preventive guidelines committee, said there were “a lot of raging controversies within the profession” about cancer screening, making it “a very confusing and disputed area”.

Professor Del Mar said one answer was for clinicians to engage in shared decision making with their patients.

“You need to put all those things on the scales to decide which way the scales are going to swing with each patient and for each screening intervention”, he said.

It was also crucial for clinicians to seek patient permission before doing a screening test. Professor Del Mar said data had shown that some doctors were adding prostate-specific antigen screening tests to a battery of other tests without advising their patients.

“This is bordering on medical negligence, particularly in light of information about potential harms”, he said.

Professor Del Mar was commenting on a US survey that found that few clinicians advised patients of the potential for harm with cancer screening.

The research letter, published in JAMA Internal Medicine, found that of 317 US patients aged 50–69 years only 9.5% said their physician had told them about the risks of overdiagnosis and overtreatment in cancer screening. (1)

About half of all survey participants (51%) told the researchers that they would not undergo screening that resulted in more than one overtreated person per one life saved from death due to cancer.

The researchers said the results indicated that clinicians’ counselling on screening fell short of patient expectations and called for improved education for health professionals about screening risks, and more detailed reporting of overtreatment risks in medical journals.

Professor Paul Glasziou, professor of evidence-based medicine at Bond University, said that in the absence of an agreed methodology to quantify the risks of harm from cancer screening, it would remain difficult for clinicians to effectively provide this information to patients. (2)

“Surveys suggest that patients want more detail, more quantification of the chances of being [overdiagnosed]. Doctors misread that, but they also have difficulty getting the numbers”, he said.

Professor Glasziou said he was not surprised that participants in the JAMA Internal Medicine study reported a lack of discussion about overdiagnosis, but suggested that 9.5% may be an underestimate.

“Given that the rates of overdetection and overdiagnosis in screening have only been quantified in the last decade, the 9.5% of patients reporting it was discussed with their doctor is not unexpected. This is likely to be an underestimate as patients may not recall that it was discussed, particularly if the last consultation was some time ago,” he said.

Professor Del Mar said clinicians had only recently come to realise the “quite significant threat” that came with cancer screening.

“It’s only recently that epidemiologists have been able to calculate the numbers and show that overdiagnosis is a problem and that the downstream consequences of overtreatment are likely to be happening as well”, Professor Del Mar said.

Improved medical education about the potential for overdiagnosis with cancer screening was needed, he said. However, he agreed that there were difficulties in communicating these risks to doctors.

Professor Glasziou said the responsibility for delivering better information to patients rests not only with clinicians but also with the media.

“We do need to have a higher awareness of this in the community and I would see it as not just as a doctor–clinician responsibility. It also needs to be a media responsibility,” he said.

“Patients expect that all cancers detected are consequential cancers. The idea of overdiagnosis is not on the media and public radar.”

1. JAMA Intern Med 2013; Online 21 October
2. Lancet Oncol 2013; 8: 1129-1138