P4-11-03: Prognosis of Pregnancy-Associated Breast Cancer: A Meta-Analysis Involving 39,415 Patients.
Authors: Azim HA , Santoro L , Russell-Edu W , Pentheroudakis G , Pavlidis N , Peccatori FA 
Published: June 2012

Background

Pregnancy-associated breast cancer (PABC), defined as breast cancer diagnosed during pregnancy or one year after is a relatively rare disease and hence considerable controversy exists regarding its prognosis compared to non-pregnancy-related breast cancer.

Methods: Two of the authors independently performed a literature search on MEDLINE and Cochrane Library with no date or language restrictions. Eligible studies were control-matched, population-based and hospital-based studies that have addressed the outcome of patients diagnosed during pregnancy or one-year afterwards. The control group was defined as patients diagnosed with breast cancer not related to pregnancy. The primary and secondary end-points were overall and disease-free survival respectively. Pooling of data was done using the random effect model. To control for potential differences between the two groups in systemic treatment and clinico-pathological features (e.g. tumor size, nodal status, ER, etc …) that could affect prognosis, we performed a sensitivity analysis by pooling the hazard ratios (HRs) of the adjusted multivariate models within each study. We also analyzed differences according to time of diagnosis (during pregnancy or post-partum), type of study and year of reporting the study. Finally, we communicated with the authors of the eligible studies to collect unpublished statistics relevant to our analysis to further refine our findings.

Results: 29 studies were included in this meta-analysis (2903 cases and 36, 512 controls). Women diagnosed with PABC had a significantly higher risk of death compared to those diagnosed with non-pregnancy-related breast cancer (pooled hazard ratio (pHR): 1.47 [95% CI: 1.30−1.65]). A sensitivity analysis including 11 studies (1222 PABC cases, 19231 controls) adjusted for differences in tumor size, nodal status and systemic treatment showed the same result (pHR: 1.44 [95% CI: 1.17−1.77]). These findings were consistent in patients diagnosed either during pregnancy (pHR: 1.30 [95% CI: 1.01−1.67]) or in the post-partum period (pHR: 1.56 [95% CI: 1.08−2.26]) with no heterogeneity observed (p=0.43). Sensitivity analyses according to the type and year of study showed the same findings. Regarding the secondary end-point, only ten studies (531 cases, 1842 controls) provided sufficient information to estimate disease-free survival, and indeed PABC patients had a higher risk of relapse compared to breast cancer controls [pHR: 1.59 (95%CI: 1.23−2.07)]. Collection of unpublished data is currently ongoing and further analyses will be presented at the meeting.

Conclusion: To the best of our knowledge, this is the largest analysis addressing the prognosis of PABC. Our results confirm that PABC is independently associated with a worse prognosis whether diagnosis is made during pregnancy or in the post-partum period. This underscores the possible impact of pregnancy on breast cancer biology. In this regard, we are currently interrogating potential biological differences between PABC patients and matched breast cancer controls at the gene expression level to elucidate the biology of this relatively rare, yet very challenging disease.

Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-11-03.