Objective: To compare stage distribution, tumor characteristics, and survival outcome in pregnancy-associated and non-pregnancy-associated breast cancer, and to evaluate pregnancy as a risk factor for mortality in breast cancer.
Methods: The California Cancer Registry (1991-1999) was linked with the California Patient Discharge Data Set to identify women with breast cancer occurring within 9 months before or 1 year after an obstetric delivery. Age-matched, non-pregnancy-associated breast cancer controls were also identified. Demographics, cancer stage, tumor size, histology, hormone receptor status, type of treatment, and survival were reviewed and compared. Predictive factors for death from breast cancer were identified using proportional hazards modeling.
Results: Seven hundred ninety-seven pregnancy-associated breast cancer cases were compared with 4,177 non-pregnancy-associated breast cancer controls. Pregnancy-associated breast cancer cases were significantly more likely to have more advanced stage, larger primary tumor, hormone receptor negative tumor, and mastectomy as a component of their treatment. In survival analysis, pregnancy-associated breast cancer had a higher death rate than non-pregnancy-associated breast cancer (39.2% compared with 33.4%, P=.002). In a multivariable analysis, advancing stage (2.22-10.76 times the risk of death for stages II-IV), race (African Americans had 68% increased risk of death over non-Hispanic whites), hormone receptor-negative tumors (20% increased risk of death over receptor-positive tumors), and pregnancy (14% increased risk of death over nonpregnant women) all were significant predictors of death.
Conclusion: Pregnancy-associated breast cancer presented with more advanced disease, larger tumors, and increased percentage of hormone receptor-negative tumors. When controlled for stage, race, and hormone receptor status, pregnancy-associated breast cancer cases had a slightly higher risk of death, even when only localized-stage disease was considered.
Level of evidence: II.