Effect of Pregnancy on Overall Survival After the Diagnosis of Early-Stage Breast Cancer

PURPOSE: To evaluate the impact of subsequent pregnancy on the prognosis of patients with early breast cancer. PATIENTS AND METHODS: One hundred eight patients who became pregnant after diagnosis of early-stage breast cancer were identified in institutions participating in International Breast Cancer Study Group (IBCSG) studies. Fourteen had relapse of breast cancer before their first subsequent pregnancy. The remaining 94 patients (including eight who relapsed during pregnancy) formed the study group reported here. A comparison group of 188 was obtained by randomly selecting two patients, matched for nodal status, tumor size, age, and year of diagnosis from the IBCSG database, who were free of relapse for at least as long as the time between breast cancer diagnosis and completion of pregnancy for each pregnant patient. Survival comparison used Cox proportional hazards regression models. RESULTS: Overall 5- and 10-year survival percentages (+/- SE) measured from the diagnosis of early-stage breast cancer among the 94 study group patients were 92% +/- 3% and 86% +/- 4%, respectively. For the matched comparison group survival was 85% +/- 3% at 5 years and 74% +/- 4% at 10 years (risk ratio, 0.44; 95% confidence interval, 0.21 to 0.96; P =.04). CONCLUSION: Subsequent pregnancy does not adversely affect the prognosis of early-stage breast cancer. The superior survival seen in this and other controlled series may merely reflect a healthy patient selection bias, but is also consistent with an antitumor effect of the pregnancy.