Women who take fertility drugs to boost ovulation may have an increased risk of developing womb cancer in later life, a study has found.
Scientists examined the medical records of 15,000 women who gave birth 30 years ago and found that those who had taken fertility-enhancing drugs were significantly more likely to be diagnosed with womb cancer than those who did not have the treatment.
Of 567 women who were given any type of drug to boost ovulation, five developed womb cancer, about three times as many as would be expected in the general population.
The 362 women who took a fertility drug called clomiphene had a four-fold increased risk of developing womb cancer. The drug prompts the body to make more eggs by inhibiting the activity of the sex hormone oestrogen.
The team, led by Dr Ronit Calderon-Margalit at Hadassah-Hebrew University in Jerusalem, also found that fertility drugs were associated with smaller but significant increases in the risk of breast cancer, malignant skin cancer and non-Hodgkin's lymphoma.
The study appears in the American Journal of Epidemiology.
Jodie Moffat at Cancer Research UK said the study was too small to draw any firm conclusions about the drug. "This study didn't include a detailed history of fertility drug use, and the number of women who developed uterine cancer was very small," she told New Scientist magazine.
Calderon-Margalit said the findings made sense, adding that the breast cancer drug tamoxifen, which works in a similar way to clomiphene, also increases the risk of womb cancer.
A spokesman for the pharmaceutical company Sanofi-Aventis, which markets clomiphene, said: "This safety concern had already been debated by experts and so far no formal conclusion has been established."
He added that the company was "committed to evaluating any new evidence and discussing with experts and healthcare authorities the appropriate information measures".
Clomiphene is considered a first step in fertility treatment for couples who have trouble conceiving when there is no obvious medical problem. If this fails, women may receive hormone injections that trigger the ovaries to produce lots of eggs at once.
