Researchers from the University of Oxford found that increases in the risk of breast cancer associated with both earlier periods and later menopause were greater for lobular than for ductal cancers, and that that the increased risk associated with a later menopause was also more marked for oestrogen-sensitive (ER-positive) cancers .
In the most comprehensive study of its kind, funded by Cancer Research UK, the researchers reanalysed original data from 117 studies worldwide, including 118, 964 women with breast cancer and over 300, 000 women without the disease.
They also discovered that starting periods earlier had a greater impact on breast cancer risk than did finishing periods later – suggesting that the effects of these factors may not simply reflect the number of reproductive cycles in a woman’s lifetime.
Dr Gillian Reeves, from The University of Oxford, said: “Our new research should helps us towards a better understanding of the way in which female sex hormones affect breast cancer risk.”
“We already knew that hormones associated with reproduction have a big impact on breast cancer risk and that starting periods early and having a late menopause increase risk but these findings suggest that sex hormone levels may be more relevant for specific types of breast cancer – ER positive tumours, and lobular, rather than ductal tumours.”
The average age in the UK for women to start their period is around 12 years old and most women start the menopause between the ages of 45 and 54.
Dr Julie Sharp, senior science information manager at Cancer Research UK, said: “This study adds some key details to our understanding of how breast cancer develops and the role that hormones play.
“The ovaries begin producing steroid hormones around the time a women starts her periods and stop rapidly around the time she begins the menopause. It’s very interesting to see that these hormones play a bigger part in the development of certain types of breast cancer and this will be important for future work in this area.”
Hazel Nunn, head of health information at Cancer Research UK, said: “Even though women can’t control the age they start their period there’s many things they can do to reduce their breast cancer risk. Keeping a healthy weight, cutting back on alcohol and having a more active lifestyle will all help to prevent the disease developing.”
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