Premenopausal women who have been diagnosed with and treated for breast cancer have understandable concerns about their fertility and possibilities for childbearing. The principal concern is the impact that pregnancy may have on the growth of microscopic disease and the possibility of recurrence. No previous studies have suggested any adverse effects of pregnancy on survival after breast cancer, and the current literature has not uncovered a link between pregnancy and breast cancer recurrence. One form of bias, called the “healthy mother effect,” has been suggested as an explanation for these findings. Women who become pregnant following breast cancer appear to be disease-free more often than their counterparts who do not become pregnant. Velentgas and colleagues evaluated whether pregnancy following breast cancer increases the risk of recurrence and mortality.

The study group was a population-based cohort (taken from two larger breast cancer studies) of women diagnosed with breast cancer. Women were eligible for this study if they had local or regional breast cancer, were 40 years of age or younger, and did not have a history of surgical sterilization. Follow-up was conducted with a questionnaire that reviewed the initial diagnosis of breast cancer, history of recurrence, menstrual status, subsequent pregnancies and other information. Deaths were determined by a routine follow-up of records, and proxy responses were obtained for patients who had died before the study. Patients who had become pregnant during the study were matched with a control group of breast cancer patients who did not become pregnant.

A total of 87 pregnancies was reported in 53 women out of the 520 who met the study criteria. Over one half of the pregnancies occurred within two years of initial breast cancer diagnosis. Of the women who became pregnant after breast cancer, 68 percent gave birth to at least one child, and 24 percent had at least one miscarriage (compared with an 18 percent predicted rate). This higher rate of miscarriage may be due to changes in hormone profiles that occur as a result of cancer treatment. Another possibility is that women with premenopausal breast cancer may simply have a higher risk of miscarriage. The rates of recurrence and mortality did not differ between women who became pregnant and those who did not, thus contributing to, but not explaining, the “healthy mother” effect.

The authors conclude that pregnancy after a diagnosis of local or regional breast cancer does not increase the risk of recurrence or mortality. However, the risk of miscarriage was higher than expected in this group, and the authors recommend further research to assess the nature of this increase.