The women now benefiting from the reduced risk are the 'baby boomers' born in the 1940s. The highest breast cancer death rates are among these women's maiden aunts, born a generation before.
Dr Valerie Beral, director of the Imperial Cancer Research Fund epidemiology unit, Oxford, told a conference in Bruges, Belgium, that social changes dictating when women have their first babies may be the key to the shifting breast cancer rates and not complicated questions of biology. She said deaths in the UK have been falling for 20 years in women now under 50 and that they have been falling for 10 years in women under 60.
Dr Beral told the Challenge of Breast Cancer conference, organised by the Lancet, that 'women born in the 1920s are seen to have the highest rates. As many as 20 per cent of them have no children and the average age of having the first child was 25.
'These are the women who were of childbearing age around the time of the Depression when many had their first baby later and many had no children at all.
'For women born in the 1940s, the average age for the first birth was 23 and the proportion not having children was only 10 per cent.'
Lack of husbands after the First World War and the trend for young marriage in the 1960s are, she believes, contributing factors to the change.
However, Dr Beral said it would follow that women born in the 1950s who are now delaying pregnancy and having first babies at an increasingly late age would again put themselves at greater risk. 'But these things may take 30 years to show up and in that time much may have changed in the prevention and treatment of breast cancer,' she said.
Dr Beral said it was an established fact that age at first birth and the number of babies that women have affected their chances of getting breast cancer in later life, but that little research had been done on the precise mechanisms of why this should happen. Dr Beral said that world-wide, breast cancer was going up by about 1 per cent a year, but that it was essential to look at the details. As poor countries became more westernised, the breast cancer rates would rise.
However, while the rates in some developed countries are declining, in others they are on the increase. 'You have to look at each country at each age and you have to see how late women have their chidren if they have them at all. It looks very much as if this is all about reproductive behaviour creating very big changes in the death rates for breast cancer.'
Her data has revealed no evidence that the contraceptive pill has caused an increase in breast cancer. 'There has been a lot of interest in oral contraception in this area, but remember that 50 per cent of women in their fifties in the UK have taken the Pill. If there was a delayed effect we would be seeing it,' she said.
In England and Wales the overall death rate for breast cancer has fallen 7 per cent since 1986 and the total number of deaths in women of all ages has also fallen from 14,008 in 1989 to 13,663 in 1992.Reuse content