Hormonal contraception used by millions of women worldwide has been linked to an increased risk of developing a rare type of brain tumour.
Prolonged use of certain drugs containing the hormone progestogen can increase the risk of meningioma – a tumour which is mostly non-cancerous – by up to five-fold, a study found.
However, experts are warning women not to stop using their birth control without consulting their doctor.
Of the progestogens included in the study, the only one used in the UK linked to a higher tumour risk was medroxyprogesterone acetate, a contraceptive injection available under the brand name Depo-Provera.
NHS data suggests there are around 10,000 prescriptions for the medication every month in England.
Prolonged use for more than a year was associated with a 5.6-fold increased risk of developing meningioma, according to the research.
“While this sounds like a very large risk it is important to realise that meningioma is rare and a five-fold increase in a rare disease is still a rare disease,” said Paul Pharoah, professor of cancer epidemiology at Cedars-Sinai Medical Center, who was not part of the study.
Of 10,000 women who are aged 30 now, about 40 can expect to be diagnosed with a meningioma before they turn 80, he said.
That figure increases to 200 for women who have used the medroxyprogesterone acetate injection, according to the study’s findings.
“This small increase in risk needs to be considered in relation to the benefits of using an injectable form of contraception,” Prof Pharoah said.
Progestogens are similar to the natural hormone progesterone. They are widely used to treat gynaecological conditions such as endometriosis and polycystic ovary syndrome, as well as in menopausal hormone therapy and contraceptives.
The new study, published in the journal The BMJ, used data from the French national health system for 18,061 women who underwent meningioma surgery between 2009 and 2018.
Each case was matched to five women without meningioma – a total of 90,305 – by year of birth and area of residence.
The researchers found that prolonged use of three progestogens was associated with a greater risk of meningioma: medrogestone (a 4.1-fold increase), promegestone (a 2.7-fold increase) and medroxyprogesterone acetate (a 5.6-fold increase).
Other progestogens were examined by the researchers, from France’s National Agency for Medicines and Health Products Safety, but were found not to increase the risk.
As it was an observational study, researchers were unable to establish whether the hormone treatments were the cause of the tumours.
However, the scientists noted that, with 74 million users of the injection worldwide, “the number of attributable meningiomas may be potentially high” in countries where the form of birth control is often used.
Further studies using other data sources are urgently needed to better understand the risks, the researchers added.
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A meningioma is usually benign but can cause serious problems in some patients due to its location in and around the brain and spinal cord.
Symptoms include a change in vision, hearing loss or ringing in the ears, loss of smell, headaches, memory loss, seizures and weakness in arms or legs.
Pfizer manufactures two medroxyprogesterone acetate injections used in the UK – Depo-Provera and Sayana Press.
The company said in a statement: “We are aware of this potential risk associated with long-term use of progestogens and, in collaboration with regulatory agencies, are in the process of updating product labels and patient information leaflets with appropriate wording.”
Dr Karen Noble, from the charity Brain Tumour Research, said: “Although this study has linked certain progestogen treatments to an increased risk of meningioma, it has also demonstrated the safety of other progestogen treatments which were shown to not increase risk.
“If you are concerned, it is recommended that you speak to your GP before stopping any prescribed treatment.”