Although medical researchers like to think of themselves as scientific and objective, they often succumb to "wishful thinking" when testing new drugs and procedures. This is especially true when there are financial incentives to show the effectiveness of a new, potentially profitable, drug.

That's what Italian researchers said in a report in the Annals of Oncology, the monthly journal of the European Society for Medical Oncology.

They stated that there is often an unconscious tendency by doctors to expect new drugs to perform better than the older ones they are being tested against.

This perception of a drug's effectiveness was named "wish bias," when it was first reported more than a decade ago. In this latest report, the research team says it may help to explain why the response rate of tumors to a new drug decreased over time.

Dr. Roldano Fossati and colleagues from the Mario Negri Institute in Milan combed through the results of 29 randomized trials that took place between 1975 and 1999. They analyzed the response rate of 2,234 women with advanced breast cancer who had been in the arms of the trials using the anti-cancer drug, doxorubicin (Adriamycin). They extracted the global (i.e. complete plus partial) response rate from all the trials.

"We found that every five years there was an 11% relative decrease in the odds of a global response and most of this decrease was in the partial response rate, where evaluation involves more subjective judgement than is involved in determining complete response," said Dr. Fossati.

Of the 29 studies they investigated, only one had used a double blind approach, and in two studies patients' records were just externally audited. A double blind study is one in which neither patients nor researchers know which control group is taking the real drug and which is taking a placebo.

"In these situations a bias due to financial and academic conflicts of interest or more subtle forms of 'wish bias' could easily arise and account for an impression that when a drug is new it does better," Fossati pointed out.

The team completed the assessment of the 29 studies to test their hypothesis that doctors' unconscious favorable attitudes to new treatments may result in a tendency to overestimate their efficacy.

According to Fossati, blinding is uncommon in many types of clinical trials. In an earlier meta-analysis by the Milan team of 189 trials involving chemotherapy and hormone therapy for metastatic breast cancer, only six involved blind evaluation and only 23 trials had involved independent or extramural assessment. There was no reason to suppose that these were not typical of cancer drug trials.

"Since indirect evidence for the existence of a wish bias emerged from our analysis, we believe that blinding should be strongly recommended for any subjective endpoint assessment such as response, time to progression of disease and so on, and the search for this kind of bias should be unremitting in order to push the medical research community to guarantee objectivity and maintain public confidence," Fossati stated.