IVF, common diabetes drug raise cancer risk

Two recent but independent British studies suggest that women who have In-Vitro Fertilisation (IVF)/Assisted Reproductive Technique (ART) may be at an increased risk of developing breast cancer, and that a common diabetes drug, pioglitazone, may raise the danger of bladder cancer.

A study published in the journal Breast Cancer Research involving 43,000 women found that those who undergo controlled ovarian stimulation – a key part of most IVF treatments – are more likely to develop dense breast tissue.

Breast density is known to be one of the strongest risk factors of breast cancer, with women who have highly dense breasts up to six times as likely to develop the disease.

Dense breast tissue contains more glandular tissue and less fat. Although it usually feels no different to the touch, it contains many more cells that are likely to turn cancerous.

Also, a new research, published in The BMJ, has found that taking the anti-diabetic drug pioglitazone which helps to control blood sugar levels in patients with type two diabetes is linked to a 63 per cent increased risk of bladder cancer.

Meanwhile, the team of scientists from the Karolinska Institute in Sweden found that women who are infertile already tend to have more dense breast tissue than fertile women – an average of an extra 1.53 cubic centimetres.
Experts suspect the root causes of infertility cause changes in the breast.

But the team found that women who underwent controlled ovarian stimulation had even more dense breast tissue – an extra 4.26 cubic centimetres.

Writing in the journal Breast Cancer Research, they said this indicates that the treatment itself – which involves hormone injections to stimulate the ovaries – may be altering the structure of the breast.

“Among infertile women, those who had gone through controlled ovarian stimulation had the highest absolute dense volume,” they wrote. “This may indicate a potential adverse effect of controlled ovarian stimulation, but could also be due to the underlying infertility.”

However, they stressed that dense breasts may not necessarily lead to breast cancer. Previous studies have found that an extra three cubic centimetres of dense tissue increases breast cancer incidence by just 2.5 per cent.

Experts said they have little to fear, because the numbers affected are so small and it is not clear whether the treatment is to blame. But some urge caution and say clinics should not overuse the technique.

Previous research, conducted by University College London (UCL), United Kingdom (U.K.) and presented at a major fertility conference last autumn, suggested that IVF might increase the risk of ovarian cancer.

Meanwhile, lead author of the diabetes drug study, Dr. Laurent Azoulay of the Centre for Clinical Epidemiology, Lady Davis Institute, Jewish General Hospital, Montreal, Quebec, Canada, said: “The results of this large population based study indicate that pioglitazone is associated with an increased risk of bladder cancer.”

Researchers wanted to assess the drug after a number of bladder cancer cases were identified among people taking the drug in a trial in 2005. Since then different studies have reported contradictory findings on the subject. They set out to compare pioglitazone with other anti-diabetic drugs.

Experts identified 145,806 patients from the UK Clinical Practice Research Database newly treated with anti-diabetic drugs between January 2000 – when pioglitazone and another medicine from the same class of drug called rosiglitazone first entered the UK market – and July 2013, with follow-up until July 2014.

Overall, 622 of these patients received a diagnosis of bladder cancer during the follow-up period.

The team of Canadian-based researchers found that compared to other anti-diabetic drugs, pioglitazone was associated with an increased risk of bladder cancer. The risk heightened with increasing duration of use and dose, they found.

No increased risk was found for rosiglitazone – the drug was withdrawn from use in 2010 due to an increased risk of cardiovascular disorders, including heart attack and heart failure.

The researchers said that patients should be informed of the risk so that they could choose whether to remain on the drug.