Results from a new study of childhood cancer statistics provide further evidence that common infections affecting mother and baby could play a key role in triggering certain types of cancer.
The research was led by Richard McNally from the University of Newcastle upon Tyne.
The team analysed a register of cancer cases diagnosed in young children over a period of 45 years. They found that a pattern emerged where two types of cancer - leukaemia and brain tumours - repeatedly occurred at similar times and geographical locations.
This 'space-time clustering' of cases is a pattern typical of diseases caused by infection, adding weight to the theory that outbreaks of infectious viruses are a potential contributory cause of cancer. Diseases caused by more constant environmental factors produce clusters of cases in one place over a much longer time period.
However, the researchers stress that people cannot 'catch cancer' as the infection is only likely to lead to cancer in a very small number of individuals who are already genetically susceptible to the disease.
McNally, who works in Newcastle University's School of Clinical Medical Sciences said: " We found that place of birth was particularly significant, which suggests that an infection in the mother while she is carrying her baby, or in a child's early years, could be a trigger factor for the cancer. These could be minor, common illnesses that are not even reported to the GP, such as a cold, mild flu or a respiratory virus.
However, this would only lead to cancer in individuals who already carry mutant cells in their body. The virus would hit this mutant cell and cause a second mutation, prompting the onset of cancers like leukaemia or brain tumours."
The findings, published in the European Journal of Cancer, may lead to better preventative measures for cancer and could result in better treatment.
Statistics for the research were taken from the Manchester Children's Tumour Register, which recorded cases of all childhood cancers in 0-14 year-olds diagnosed between January 1954 and December 1998. It covers the areas of Southern Cumbria, Lancashire, Greater Manchester, North West Derbyshire and North Cheshire.
The researchers carried out a sophisticated form of statistical analysis for the study, which is the first of its kind. They sought to establish where there was a pattern of certain types of cancers in relation to the time and place of childrens' birth and the time and place of where children were living when diagnosed.
Most significant were the clusters of leukaemia and central nervous system tumours found around time and place of birth.
In these clusters, there were eight per cent more cases of these cancers than could be explained by chance.
Moreover, clusters of acute lymphoblastic leukaemia and the brain tumour astrocytoma were also found around time and place of birth - here there were 13 per cent more cases than expected.
There are theories that suggest environmental influences, such as viral infections, are part of the cause of cancer, in addition to genetic susceptibility. This research provides further evidence that this may be the case.
John Toy, Cancer Research UK's medical director, said: " These findings provide more clues to a link between viruses and some types of childhood cancer, but we need more evidence before we can be sure. Reassuringly for mums, children who are introduced to day care or who are more socially active during their first year of life have been found to be at lower risk of childhood leukaemia. This may be because their immune systems have been strengthened by being exposed to a wide variety of infections at an early age."
Source: University of Newcastle upon Tyne, 2005