Some birth control pills may temporarily increase a woman’s risk of breast cancer by as much as 50 per cent, an American study has found.
Women who, in the past year, had taken contraceptive pills which had a high or moderate dose of oestrogen, as well as those containing certain other hormones, had a 50 per cent increased risk of breast cancer, research involving more than 1,100 cancer patients revealed.
Any increased risk of breast cancer from taking birth control pills will have disappeared within 10 years of coming off the pill, experts said.
Pills with a low dose of oestrogen did not increase breast cancer risk. Most commonly used contraceptive pills contain low to moderate doses of oestrogen.
The findings, which reinforce previous studies into a complex area of medicine, have been welcomed by experts who said they provided insights into the impact of different formulations of birth control.
The researchers, from the Fred Hutchinson Cancer Research Center, also said that their findings should be treated with caution because breast cancer was rare among young women most likely to use the pill and that oral contraceptives also carried “numerous established health benefits”.
The study is published in Cancer Research, a journal of the American Association for Cancer Research, today.
Dr Caroline Dalton, senior policy officer at Breakthrough Breast Cancer, said that women who had any concerns about starting or stopping the pill should talk through the options with their doctor.
“Levels of oestrogen in the combined pill have decreased over the past 30 years. Whilst the researchers state that these findings require further investigation, we are a little closer to finding out whether or not newer, lower-dose pills are associated with the same risk as the higher-dose formulations more commonly used in the past,” she said.
“However, it is important to note that breast cancer is rare in women under the age of 40, regardless of whether or not they use the contraceptive pill. In addition, 10 years after coming off the pill any increased risk will have disappeared leaving the chance of developing breast cancer at around the same level as those who’ve never taken the pill.”
The study compared the use of oral contraceptive pills among 1,102 women diagnosed with breast cancer between 1990 and 2009, with a control group of 21,952 people. They found that recent use of contraceptive pills increased breast cancer risk by 50 per cent compared to women who had never or formerly used them.