About 9400 brain tumours were diagnosed in 2011. Astrocytoma – a type of cancer called a glioma – is the most common, accounting for 34% of cases. Approximately 80% of astrocytomas are an aggressive subtype called glioblastoma multiforme. Research has suggested that long-term users of hormonal contraceptives are nearly twice as likely to develop gliomas as non-users.
Epidemiological studies reported either no link between contraceptive use and glioma or a weak protective effect in women. However, these studies enrolled only post-menopausal women or small numbers of premenopausal women. The new study examines the link in younger women.
Researchers identified 317 women aged 15 to 49 years with a first-time diagnosis of glioma. They matched each case with eight controls. Women who had used hormonal contraceptives were 50% more likely to have a glioma than controls. Women who used hormonal contraception for at least five years were 90% more likely to develop a glioma. The link was stronger for use within the last two to five years (odds ratio [OR] 1.7) than for use more than five years previously (OR 1.2). The researchers disregarded contraceptive use in the last two years to avoid potential confounders.
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