Certain biases may exist in observational studies that compare outcomes of different cancer therapies, making the results questionable.
That is the conclusion of a new study published in the June 1, 2008 issue of CANCER, a peer-reviewed journal of the American Cancer Society. The research suggests that observational studies should include more thorough information and should be better designed to minimize inaccuracies.
Clinical trials are considered the gold standard for demonstrating the effectiveness of new treatments for cancer, but observational studies, which do not involve randomization but where available data are nonetheless analyzed to make treatment comparisons, have also been used to provide information on how well patients respond to particular drugs. Many investigators perform these types of studies by analyzing data from the Surveillance, Epidemiology and End Results (SEER) Tumor Registry, a national population-based cancer registry that collects cancer-related information.
To determine the accuracy of observational studies on cancer treatments, Dr. Sharon H. Giordano of the University of Texas MD Anderson Cancer Center in Houston and her colleagues compared the effectiveness of different cancer therapies in terms of prolonging survival in patients, using data from the SEER registry. They presented several examples, including re-analyses of previously published data. In all cases, they came up with improbable results, indicating how easy it is to generate questionable results when conducting an observational study.
In their first analysis, the researchers looked at data on a hormone therapy called androgen deprivation in men with stage III prostate cancer. Randomized clinical trials have shown that androgen deprivation can improve survival in these patients. When the investigators analyzed data from the SEER registry of more than 5,000 men, they found that men treated with androgen deprivation actually had a higher risk of death from prostate cancer than men who did not receive the therapy.