When a woman who is taking or has previously taken HRT develops breast cancer there is no way of knowing for certain whether or not HRT caused the cancer.

Large trials have shown that in women over the age of 50, who take HRT for more than a year or two, their risk of breast cancer is increased. The longer they take it the greater the risk.

Women who never take HRT

• For every thousand women aged 50 who never take HRT, 32 will develop a breast cancer by the age of 65.

Women who take HRT

• For every thousand women aged 50 who take HRT for the next five years between 33 to 38 will develop a breast cancer by the age of 65 (an extra 1-6 cases for every thousand women taking the HRT).
• For every thousand women aged 50 who take HRT for the next 10 years between 37 to 51 will develop a breast cancer by the age of 65 (an extra 5 to 19 cases for every thousand women).
• If a woman over 50years who has been on HRT for more than 2 years, stops taking HRT her risk of breast cancer gradually reduces, and within 5 years is the same as in women who have never taken HRT.
• For women who have an earlier menopause, before the age of 50, and take HRT, their risk of developing breast cancer seems to be about the same as other women who have not had their menopause.

These trials leave no doubt that taking HRT long-term, after the age of 50, increases a woman's risk of breast cancer. But the results are based on statistics from large numbers of women and cannot be used to predict what will happen to any one individual. So if you are under 50, and have been taking HRT, and have breast cancer your cancer is unlikely to be linked with HRT. If you are over 50 years and have been taking HRT for more than a year or two, and have developed breast cancer, then HRT may have contributed to it but there is no way of being certain. Taking HRT is a personal choice and women with the help of their doctor can weigh up the pros and cons for them.