The risk of breast and gynaecological cancer in women with a diagnosis of infertility

A nationwide population-based study

Infertility is one of the most common health problems impacting young people, affecting about one in seven couples who are trying to conceive1. About one half of cases of infertility are due to female causes, with hormonal disorders affecting ovulation, including polycystic ovary syndrome (PCOS), being the most common.

Cancers of the ovary, endometrium and breast are related to several hormonal and reproductive risk factors, and a number of previous studies have investigated the associations between fertility treatments using hormonal stimulation and the risk of breast and gynaecological cancers. However, since both causes and consequences of infertility can influence cancer risk, the relationship is complex.

Now the results of a new Swedish study2 has created a more comprehensive picture of the association between infertility and the risk of ovarian, endometrial and breast cancer in a large population of women. The study also aimed to investigate if such associations could be explained by either ovulatory disturbances, endometriosis or nulliparity.

The study population comprised 2,882,847 women born 1942–1992 who were registered in the population-based Swedish Multi-Generation Register. Of the women in the cohort, 117,500 (4.1%) had a diagnosis of infertility. The mean follow-up time was 23.4 years among fertile women and 25.8 years among women with infertility. Among the infertile women 16.4% were diagnosed with ovulatory disturbances and 11%

with endometriosis, compared to 1.5% and 2.0% respectively of women designated as fertile.

Results of the research indicate that infertile women had higher risks of ovarian and endometrial cancer, but the risk of breast cancer was not found to be increased.

• Breast cancer: The study found no increase in breast cancer risk among women with infertility or related diagnoses. These findings were in line with other previous studies on breast cancer risk in women with infertility3
• Ovarian cancer: Infertile women had a higher incidence rate of ovarian cancer in our study. These results are similar to those of a previous large prospective cohort study4
• Endometrial cancer: A higher risk of endometrial cancer was found among infertile compared to fertile women. The risk was also higher among women diagnosed with ovulatory disturbances, especially in combination with infertility. This risk appeared to be higher among nulliparous women and only evident before menopause

In their discussion of the results the researchers say:  “The results from this large population-based study suggest that infertile women may have a higher risk of certain cancers, such as gynecological cancers, but not of breast cancer.”

The data also confirms findings of previous studies on the increased risk of ovarian cancer in women with infertility and endometriosis, and support evidence that ovulatory disturbances, probably due to underlying polycystic ovary syndrome, increase the risk of endometrial cancer in infertile women.