IVF increases the risk of breast cancer in older women, a study suggests.
Women over 40 who have had the treatment are 65pc more likely to develop the disease than people of the same age who have not had it, according to researchers in Denmark.
Scientists believe oestrogen given to women to stimulate the ovaries into producing more eggs in preparation for IVF may explain the cancer link.
Prof Geeta Nargund, of St George's Hospital, London, said: "This is a finding of great significance.
"This is a wake-up call about the use of high dose stimulation in IVF, especially in women over the age of 40. We must act now as a precaution."
The team of researchers at Copenhagen University tracked 59,000 women who had fertility treatment, then compared them to 567,000 females of equal age who had not.
Over the 21-year study period less than 1pc of the 626,000 women were diagnosed with breast cancer.
The likelihood of developing the disease overall was low, even after adjusting for other risk factors. The study was presented at the European Society of Human Reproduction and Embryology conference in Vienna.
Meanwhile, a new urine test for prostate cancer could revolutionise treatment and prevent unnecessary biopsies.
The test is much more sensitive than current methods, picking up how aggressive the disease is and at what point men will need treatment.
It is designed for men who are suspected of having prostate cancer, as well as those already diagnosed with low risk disease who are on a "watch and wait" approach known as active surveillance.
For men suspected of having prostate cancer, the test can work out which men have aggressive or intermediate levels of the illness and can rule out those without cancer.
This cuts down the need for a barrage of tests, including blood tests, a physical examination known as a digital rectal examination (DRE), an MRI scan or a biopsy.
In the case of men already on active surveillance, the test could cut follow-up appointments from once every year to once every five years.
At present, medics can struggle to identify patients with an aggressive form of the disease who need immediate treatment from those who are low risk.