This site is intended for health professionals only

A third of breast cancer trials ‘have evidence of bias’

A third of trials involving breast cancer treatments have evidence of spin or bias in their reporting, raising questions over the benefits of treatments, according to a new review.

Canadian oncologists found 33% of breast cancer clinical trial papers were reported as having positive results despite not showing a statistically significant difference in the primary end point.

In their findings, published in the journal Annals of Oncology this week, they also found two-thirds of studies showed bias by under-reporting the toxic effects of treatment.

The findings come from a review of 164 randomised controlled Phase III trials of breast cancer treatments by researchers at the Princess Margaret Cancer Centre, Toronto, and the University of Toronto, Canada.

Positive results were often inferred from secondary endpoints, and the lack of any benefit on primary endpoint was not mentioned in the abstracts of more than one in four of these trials .

The authors concluded: ‘These reports were biased and used spin in an attempt to conceal that bias.’

‘A possible explanation for this could be that the investigators, sponsors or both, prefer to focus on the efficacy of the experimental treatment and downplay toxicity to make the results look more attractive.’

The analysis also found suggestions that in some trials researchers had been shifting the goalposts and changing the primary endpoint mid-trial to emphasise more positive results.

‘Among these trials, there was a trend towards change of the primary endpoint being associated with positive results, suggesting that it may be a strategy to make a negative trial appear positive,’ the authors added.

Study researcher Professor Ian Tannock, medical oncologist and senior scientist in the Division of Medical Oncology and Hematology at the Princess Margaret Cancer Centre, said there was a need for study authors, journals and clinicians who review the articles for journals to be more rigorous in encouraging unbiased reporting of trial results and in enforcing guidelines.

Professor Tannock said: ‘Better and more accurate reporting is urgently needed. Journal editors and reviewers, who give their expertise on the topic, are very important in ensuring this happens.’

‘However, readers also need to critically appraise reports in order to detect potential bias. We believe guidelines are necessary to improve the reporting of both efficacy and toxicity.’

Dr Malcolm Kendrick, a GP in Macclesfield, said the study showed a ‘systemic problem’ in the reporting of clinical studies.

He said: ‘There’s a huge issue. There’s a real need now for pharmaceutical companies and other researchers to honestly report their drug adverse effects and not try to hide them, because otherwise who knows what kind of effects they are having in the real world in real patients?’

Annals of Oncology 2013, online 10 January. doi:10.1093/annonc/mds636