ONLY YOUNGER WOMEN HAVE INCREASED BREAST CANCER RISK AFTER IVF 

June 28, 2012 — Women who began in vitro fertilization (IVF) treatment before the age 24 years may have a slightly increased rate of breast cancer. However, when all ages of women were grouped together, IVF was not associated with an increased risk for breast cancer.

Louise M. Stewart, BSc, from the School of Population Health, University of Western Australia in Crawley, and colleagues reported the results of a population-based cohort study in an article published online May 28 in Fertility and Sterility. The study made comparisons within a cohort of women seeking infertility treatment.

The authors evaluated the linked hospital and registry data of all women (n = 21,025) aged 20 to 44 years seeking hospital investigation and treatment for infertility in Western Australia from 1983 through 2002. An effort was made to minimize loss to follow-up by excluding women with an out-of-state address on their hospital records.

The mean duration of follow-up in the younger members of the cohort was 17.5 years (95% confidence interval [CI], 17.4 - 17.6) compared with 15.9 years (95% CI, 15.8 - 16.0) for older members (P < .001). Younger was defined as younger than 31 years at first infertility admission, and older was defined as aged 31 years or older.

The article described an unadjusted hazard ratio of 1.59 (95% CI, 1.05 - 2.42) of breast cancer for women who began hospital IVF at aged 24 years compared with women of the same age who had infertility treatment but no IVF. When the authors adjusted for age at first birth, the hazard ratio was 1.47, but was no longer statistically significant (95% CI, 0.96 - 2.26). However, when they adjusted for age at first birth and for multiple deliveries, the hazard ratio was 1.56, which was statistically significant (95% CI, 1.01 - 2.40).

Dr. R. Stan Williams, immediate past president of the Society for Assisted Reproductive Technology, spoke withMedscape Medical News about the research. He pointed out that, "the vast majority of women who undergo IVF are over the age of 28." Thus, the concern of increased risk for breast cancer would only be relevant for a small percentage of women seeking IVF.

Dr. Williams, who was not involved in the work, also explained that hazard ratios are not particularly helpful for clinicians and patients trying to evaluate risk. Rather, what the public needs to know is the absolute risk associated with IVF. Using the data presented in the article, he estimated that IVF would lead to 2 to 3 extra cases per 10,000 women older than 16 years, but only in women age 28 or younger at the time of treatment.

Dr. Williams acknowledged that he was surprised to see the increased risk. He explained that he did not understand how a single week of elevated estrogen could result in an increased risk for breast cancer.

The study did not include an analysis of types or doses of fertility drugs. The authors propose extending the research to examine the relationship between IVF dose and breast cancer rate.

The authors also confirmed the well-known association between age at first delivery and breast cancer risk. The delivery of a first child late in reproductive life is associated with an increased breast cancer risk whether assisted by IVF or not.

One author is a medical director and board member of the board of Fertility Specialists of Western Australia, is medical advisory board member of MSD Australia and Merck Serono Australia, is a shareholder in Western IVF, and has received financial support to attend European Society for Human Reproduction and Embryology meetings. The other authors and Dr. Williams have disclosed no relevant financial relationships.

Fertil Steril. Published online May 28, 2012. Abstract