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.
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.
For example, selection bias occurs when patients with poorer prognoses are more likely to receive a more efficacious drug, or when patients with better underlying health are more likely to receive a more toxic treatment because they are more likely to tolerate it.
The authors concluded that their findings “suggest that the results of observational studies of treatment outcomes should be viewed with caution.” They recommended that analyses of observational data should at a minimum attempt to segregate patient outcomes into those that could possibly be due to the treatments vs. those that could not. Many observational studies on cancer treatments only report death rates from all causes and do not specify cancer-related deaths.