DOZENS of new cancer drugs made available to patients in Europe between 2014 and 2016 were approved on the basis of clinical trials found to be at "high risk of bias", researchers have warned.

They said the treatment effects may have been exaggerated and called for stricter rules on how new drugs were judged, including a renewed focus on patients' overall survival instead of measures such as progression-free survival or disease response which "do not consistently translate to survival gains or quality of life benefits".

NHS Scotland spent £1.7 billion on drugs in 2016/17, an increase of nearly 20 per cent in five years.

Cancer drugs are driving most of the increase in pharmaceutical spending across the NHS, but the researchers noted that there is "no association between magnitude of benefit and drug price".

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Among the drugs linked to randomised control trials deemed to have a "high risk" of bias were a number approved for routine or restricted use on NHS Scotland.

In the case of leukaemia drug, pegaspargase (Oncaspar), all five studies examined were considered high risk, while breast cancer drug palbociclib (Ibrance) was approved on the basis of two studies whose results are considered potentially unreliable.

The studies behind skin cancer drug trametnib (Mekinst) and immunotherapy treatment nivolumab (Opdivo) were also criticised by the researchers.

The findings are published today in the British Medical Journal and the analysis was led by the London School of Economics.

In a linked editorial, Australian-based researchers argue that uncertainty and exaggeration of the evidence that supports approval of cancer drugs “causes direct harm if patients risk severe or fatal adverse effects without likely benefit, or forgo more effective and safer treatments.”

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Inaccurate evidence also leads to intangible harms, which encourage false hope and create a distraction from needed palliative care, they add.

Before drugs can be prescribed on the NHS, they must be approved by the European Medicines Agency (EMA).

The EMA bases its decisions on clinical trial data submitted by pharmaceutical manufacturers.

Between 2014 and 2016, the EMA approved 32 new cancer drugs on the basis of 54 pivotal studies.

Of these, 41 were randomised controlled trials - considered the gold-standard for research because the new drug is compared against a placebo, and participants do not know whether they are on the medication or the placebo.

However, the researchers found that 19 of the 41 RCTs (49%) were at high risk of bias "based on their design, conduct or analysis".

This included problems such as participants not being properly randomised, or a lack of "blinding" - a technique which means neither the participants nor the researchers themselves know who is on the drug or the placebo.

The BMJ study said these types of double-blind trials were less prone to bias, but more expensive to organise.

Half of the new cancer drugs were also approved on the basis of a "single pivotal study", said researchers, with only seven backed by two or more RCTs.

They added: "Recently, cancer drugs have comprised the single largest category of new drug approvals in Europe. In 2017, more than a quarter (24/92) of EMA approvals were for cancer drugs.

"There is considerable debate and controversy about the therapeutic and economic value of these drugs.

"Our recent research showed that most new cancer drugs were approved by the EMA without evidence of benefit on overall survival or quality of life."

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The BMJ researchers also found that only 10 of the 41 RCTs measured results on the basis of overall survival.

They noted that since the 1970s, clinical trials have increasingly looked to alternative ways of measuring a drug's effectiveness in cancer patients, such as progression-free survival - the length of time without relapse.

These types of studies are cheaper and easier to organise because they can use smaller sample sizes and results are generally reported earlier - clinical trials are on average 11 months shorter than those using overall survival as the outcome.

However, the BMJ study found that bias was more common where these alternative measures were used, and lowest in those which assessed drugs on overall survival.

They concluded: "Taken together, these findings support more widespread use of overall survival as the primary endpoint in pivotal trials of new cancer drugs.

"Randomised control trials with overall survival endpoints were less likely to be at risk of bias in our sample."