In vitro fertilization and breast cancer: is there cause for concern?

To examine the incidence rate of breast cancer in a cohort of women undergoing treatment for infertility, comparing the rate in women who had in vitro fertilization (IVF) with those who did not.

Population-based cohort study using linked hospital and registry data.

Hospital.

All women aged 20-44 years seeking hospital investigation and treatment for infertility in Western Australia during the period 1983-2002 (n = 21,025).

None.

Hazard ratios (HRs) for breast cancer.

There was no overall increase in the rate of breast cancer in women who had IVF (HR 1.10, 95% confidence interval [CI] 0.88-1.36), but there was an increased rate in women who commenced IVF at a young age. Women who commenced hospital infertility treatment at 24 years and required IVF had an unadjusted HR of breast cancer of 1.59 (95% CI 1.05-2.42) compared with women of the same age who had infertility treatment but no IVF. When adjusted for late age at first delivery, which is associated with an increased rate of breast cancer, and delivery of twins and higher-order multiples, which is associated with a decreased rate of breast cancer, the HR remained elevated at 1.56 (95% CI 1.01-2.40). Hazard ratios were not elevated in women who commenced treatment at age 40 and required IVF (adjusted HR 0.87, 95% CI 0.62-1.22).

Commencing IVF treatment at a young age is associated with an increased rate of breast cancer.