Cancer studies may be biased

       Studies on whether mobile phones can cause cancer,especially brain tumours, vary widely in quality and there may be some bias in those showing the least risk, researchers reported on Tuesday.
       So far it is difficult to demonstrate any link, although the best studies do suggest some association between mobile phone use and cancer, the research coordinated by South Korea's National Cancer Center found.
       Dr Seung-Kwon Myung and colleagues at Ewha Women's University and Seoul National University Hospital in Seoul and the University of California, Berkeley,examined 23 published studies of more than 37,000 people in what is called a meta-analysis. Results often depended on who conducted the study and how well they controlled for bias and other errors.
       "We found a large discrepancy in the association between mobile phone use and tumour risk by research group, which is confounded with the methodological quality of the research," they wrote in the Journal of Clinical Oncology .The use of mobile and cordless phones has exploded in the past 10 years to an estimated 4.6 billion subscribers worldwide, according to the UN International Telecommunication Union.
       Research has failed to establish any clear link between the devices and cancer.
       The latest study, supported in part by the US Centers for Disease Control and Prevention, examined cases involving brain tumours and others including tumors of the facial nerves, salivary glands and testicles as well as non-Hodgkin's lymphomas.
       It found no significant association between the risk of tumours and overall use of mobile phones, including cellular and cordless phones.
       The South Korean team said "high quality" studies that blinded participants against bias found a mildly increased risk of tumours among mobile phone users. An increased risk of benign tumours was also found in people who used the phones for a decade or longer.
       The "high quality" studies were funded by the Swedish Work Environment Fund,the Orebro Cancer Fund and the Orebro University Hospital Cancer Fund, the research team said.
       Funding for some of the lower-quality studies included two industry groups,the Mobile Manufacturers Forum and the Global System for Mobile Communication Association.