IVF Did Not Increase Breast Cancer Incidence

Results from a new long-term study indicated that undergoing fertility treatment with in vitro fertilization (IVF) did not increase women’s risk for breast cancer compared with other fertility treatments or with women in the general population.

“These findings are consistent with the absence of a significant increase in the long-term risk of breast cancer among women treated with these IVF regimens,” wrote researcher Alexandra W. van den Belt-Dusebout, PhD, of the Netherlands Cancer Institute, Amsterdam, and colleagues in JAMA.

Breast cancer risk is known to be affected by exogenous and endogenous estrogens and progesterone. Since IVF procedures temporarily decrease estradiol and progesterone levels and increase hormone levels, it was thought that IVF might affect breast cancer risk. However, prior studies looking at an association between IVF and breast cancer have been inconclusive.

For this study, Dusebout and colleagues looked at data from a cohort of women treated at 12 IVF clinics in the Netherlands. The cohort included 19,158 women who underwent IVF between 1983 and 1995 and 5,950 women who started other fertility treatments between 1980 and 1995 (non-IVF group). The median age of the women at the end of follow-up was 53.8 for the IVF group and 55.3 for the non-IVF group.

With a median follow-up of about 21 years, 839 cases of invasive breast cancer and 109 cases of ductal carcinoma in situ were diagnosed. The rate of breast cancer per 100,000 women was 163.5 for IVF, 167.2 for non-IVF, and 163.3 for the general population. The rate of breast cancer was not increased among women in the IVF group (standard incidence ratio [SIR], 1.01 [95% CI, 0.93–1.09]) or the non-IVF group (SIR, 1.00 [95% CI, 0.88–1.15]) compared with women in the general population.

There was no increased incidence of breast cancer with a longer time since treatment among the IVF group (SIR, 0.92) or the non-IVF group (SIR, 1.03).

The researchers did find a few significant associations. There was a significant decrease in breast cancer among women who did not bear children (SIR, 0.86 [95% CI, 0.76–0.97]), but there was no increased risk among those women who did. Additionally, risk for breast cancer was significantly lower among women who had undergone 7 or more IVF cycles (hazard ratio [HR], 0.55) compared with women who underwent 1 to 2 cycles after poor response to the first cycle (HR, 0.77).

Dusebout and colleagues pointed out that because the results are based on IVF treatments done prior to 1995, the generalizability may be limited.

“During the study period, the number of IVF cycles and, consequently, the number of ampules of gonadotropins used increased until 1990 and decreased thereafter,” they wrote. “Because more recent IVF regimens largely consist of protocols with antagonists and shorter periods of downregulation (possibly associated with less risk reduction), and improved success rates (associated with fewer cycles), it is uncertain how study results generalize to more contemporary IVF treatment.”