Cellphone use and increased risk of cancer is a subject around which there is continuing research. Concerns have been raised regarding cellphones as possibly associated with increased risk of some cancers. A team of researchers from Imperial College London has looked at the risk of early childhood cancers, such as leukaemias and brain tumours, and mothers’ exposure during pregnancy to mobile phone base stations (masts). Analysis of the cancer registry, the national birth register data and the database of base station antennas allowed a case-control comparison. The study involved 1397 cases of cancer in children aged 0-4 years (1999-2001) and 5588 children without cancer, individually matched by sex and date of birth (four controls per case). The study authors report that "Mean distance of registered address at birth from a macrocell base station … was similar for cases and controls … as was total power output of base stations within 700m of the address.” In the study report, published in the 22 June 2010 British Medical Journal (BMJ 2010;340:c3077), the authors concluded, “There is no association between risk of early childhood cancers and estimates of the mother’s exposure to mobile phone base stations during pregnancy.”