A woman's risk of developing cancer is up to one fifth higher for those with fertility issues compared with those without these problems, according to new research.
The study, published in Human Reproduction, analysed records from a US database of health insurance claims from between 2003 and 2016. Looking at data from 63,000 infertile women and 3 million fertile women, the researchers found that those in the infertile group were 18 percent more likely to develop cancer compared with fertile women of the same age.
'We do not know the causes of the increase in cancer that we found in this study, whether it might be the infertility itself, the causes of the infertility, or the infertility treatment. We can only show there is an association between them,' said study leader, Dr Gayathree Murugappan of Stanford University, California.
Previous studies have questioned whether hormone-altering drugs for fertility treatment may increase women's predisposition to cancer. However, this study reports an increased risk among infertile women for both hormone-associated cancers, such as ovarian and uterine cancer, and cancers that are not hormone-associated, such as lung, thyroid and liver cancer.
There were some limitations to the study. The infertile cohort included a mixture of women some of whom had had a diagnosis or treatment for infertility, but some who had only received testing for infertility. As a result, the underlying reason for the association found between infertility and cancer remains unclear.
The authors of the study also noted that while infertility was linked to an increased cancer risk of 18 percent, the absolute values for this risk were more modest: at 2 percent versus 1.7 percent. In addition, the follow-up period was only four years.
'We need to carry out further research with longer follow-up to determine what factors may be influencing the long-term risk of cancer for infertile women,' said Dr Michael Eisenberg, a study author also at Stanford.
There are several theories that could explain the long-term cancer risk observed in this study. For instance, infertility and cancer in women may have a common genetic basis. Alternatively, in some cases infertility could be a warning sign of cancer in women.
Professor Justin Stebbing from Imperial College London, who was not involved in the research, said: 'We not only need to carry out further research with longer follow-up to determine what factors may be influencing the long-term risk of cancer for infertile women, but we need to understand how and why this occurs. Are there cancer-causing genes for example that may predispose people to infertility and do we need to better follow up infertile women to watch them more closely for cancer?'