There is a marked east-west divide in the incidence of certain cancers on the island of Ireland, the second all-Ireland cancer report shows.
The area along the eastern side of the country has a higher number of cases of breast, colorectal and lung cancer than would be expected. Prostate cancer rates in men and stomach cancer rates are also higher in the east compared with the west.
Emphasising the lack of geographical difference in the incidence of lymphoma (cancer of the lymphatic system) in adults and in the incidence of childhood cancers, both of which are radiation sensitive, Dr Anna Gavin, director of the Northern Ireland Cancer Registry told The Irish Times: "There is no evidence in the data analysed of a negative health impact on the population of Ireland from the [British Nuclear Fuels] plant at Sellafield."
Commenting on the regional differences, Dr Harry Comber, director of the National Cancer Registry in the Republic, said: "There are a number of different phenomena at work which explain the differences in breast, lung and colorectal cancer rates."
He said the high rates of breast cancer in Dublin and Kildare may reflect the greater availability of mammography in the area.
"We cannot say why colorectal cancer rates are higher, particularly in the north midlands. The presumption is that it is related to diet but we do not have enough information to be certain."
Dr Comber said the higher rates of lung cancer in the east and north east were linked to the increased prevalence of smoking in urban areas.
"Understanding why regional variations exist, and targeting prevention programmes to these regions and populations at higher risk, should be a public health priority," the report says.
The report, which says there are over 19,000 new cancer cases and 11,000 cancer deaths throughout the island each year, also notes a disparity between the Republic and Northern Ireland in the number of cases of prostate cancer in men.
It reveals the incidence of prostate cancer has increased by 33 per cent over a six-year period from 1994-2000 in the Republic. In Northern Ireland during the same period there was no change in incidence.
In addition, death rates from the disease fell by 12 per cent in Northern Ireland while they remained unchanged in the Republic.
However, both Dr Gavin and Dr Comber said the differing rates may be misleading.
"The last year of Northern Ireland data showed a 20 per cent increase in the number of cases of prostate cancer cases," Dr Gavin said, adding that if this trend continues the disparity between the North and the Republic will narrow.
The report points to the unproven role of testing for prostate specific antigen (PSA) as a likely cause for the disparity.
"PSA tests increase the number of cases reported and increase the rates. Since the value of PSA testing is still unproven, there is wide variation in its use. Differing incidence rates in Ireland, the EU and the US may be a reflection of this variation in PSA testing," it says.
Welcoming the ban on tobacco use in the workplace in the Republic, Dr Gavin said she was concerned the lack of a similar ban in Northern Ireland could see it trailing behind in lung cancer incidence in years to come.
"Lung cancer rates in men are dropping and those in women are static in the North at present."
However, both cancer registry directors emphasised the significant time lag between stopping smoking and a corresponding drop in deaths from the disease. The highest rates for lung cancer were seen in Dublin, Belfast and Derry.
"I will recommend at the launch today that further focused research is needed to look at the reasons for the high rates of colorectal cancer in the north midlands," said Dr Comber.
Both cancer registries have already been awarded research grants from the Health Research Board and the Northern Ireland Research Office.