A new study says that more often than not cancer treatment studies that are observational in nature may be adversely affected by certain biases.
Dr. Sharon H. Giordano and her colleagues at the University of Texas MD Anderson Cancer Center in Houston set out to determine the accuracy of observational studies on cancer treatments, and compared the effectiveness of different cancer therapies in terms of prolonging survival in patients.
They used data from the SEER registry for the purpose.
In their first analysis, the researchers focussed their attention on a hormone therapy called androgen deprivation in men with stage III prostate cancer.
While randomised clinical trials showed that androgen deprivation could improve survival in patients, their analysis 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.
Thereafter, the researchers re-analysed data from a previously published study of more than 43,000 men with localized prostate cancer who were treated compared with men who were not treated.
Just like the original study, the researchers' analysis revealed that men who were treated for prostate cancer experienced lower mortality rates. They, however, found that in many cases, the cause of death was due to something other than prostate cancer, like diabetes or pneumonia.
The researchers then re-analysed data from a previously published study on the effects of fluorouracil-based chemotherapy for colon cancer, and came to the same conclusion as the original research study-that chemotherapy for node positive colon cancer is associated with improved survival.
However, their analysis also found that the link between the treatment and survival was strongest for non-cancer deaths, which presumably are not related.
The researchers said that the improbable results found in their three analyses were due to selection biases occurring when patients are treated.
They say that selection bias generally 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: "(The findings) suggest that the results of observational studies of treatment outcomes should be viewed with caution."
The findings appear in the journal CANCER.