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18-03-2019 | Risk factors | News

Infertility linked to increased risk for multiple cancer types

medwireNews: Women with infertility have a significantly higher risk than those without for both hormonal and nonhormonal cancers, but the absolute risk in both groups is low, shows an analysis of US insurance claims data.

Among 64,345 women who had an infertility diagnosis or were undergoing infertility testing or treatment between 2003 and 2016, 2.0% developed cancer during an average 3.8 years of follow-up.

This was significantly higher than the rate of 1.8% observed among 3,128,345 non-infertile patients receiving routine gynecologic care during 3.9 years of follow-up and resulted in a hazard ratio (HR) of 1.18 after adjustment for age, year, nulliparity, race, smoking, obesity, number of medical visits per year, and education level.

However, Gayathree Murugappan (Stanford Hospital and Clinics, California, USA) and co-investigators point out that the low incidence overall “translates into a very modest increase in absolute risk of 1/49 compared to 1/59 for infertile and non-infertile patients, respectively.”

In line with previous findings, the incidence of hormonal cancers was significantly higher among the infertile women than among the non-infertile women, at adjusted HRs of 1.78 for uterine cancer (0.10 vs 0.06%) and 1.64 for ovarian cancer (0.14 vs 0.09%).

But the team also observed an increased risk for nonhormonal cancers among the infertile group including cancers of the liver and gallbladder, lung, and thyroid, as well as leukemia, at adjusted HRs of 1.59, 1.38, 1.29, and 1.55, respectively.

Of note, breast cancer was the most common cancer diagnosed in both groups and the incidence was similar (0.51 vs 0.49%).

A subgroup analysis of women who had a pregnancy and subsequent delivery during the enrollment period in both the infertile (34.2%) and non-infertile (20.0%) groups showed that the risk for cancer overall remained significantly higher in the infertile group, but between group differences were diminished for uterine, ovarian, lung, and liver and gallbladder cancers.

“As some of these cancers are hormone mediated, it does suggest a possible mechanism behind the seemingly protective effect of childbearing among infertile women who succeed in fertility treatment,” Murugappan and co-authors remark.

A second subgroup analysis, which excluded women with polycystic ovary syndrome (PCOS) and endometriosis gave similar results to the overall analysis, with the exception of uterine cancer, which was no longer more common among the women in the infertile group.

The researchers say this “suggests that PCOS/endometriosis may confound the relationship between infertility and uterine cancer.”

Writing in Human Reproduction, Murugappan et al highlight the importance of remembering “that cancers in reproductive age women are, overall, rare events and the conclusions of our subgroup analysis are limited by the low incidence of the outcomes of interest.”

They conclude: “While the absolute increase in cancer risk with infertility is small, this increase was seen within only 4 years of infertility diagnosis, strongly supporting the need for further study to determine what factors influence the long-term cancer risk for infertile women.”

By Laura Cowen

medwireNews is an independent medical news service provided by Springer Healthcare. © 2019 Springer Healthcare part of the Springer Nature group

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