Abstract P3-08-11: Pregnancy after breast cancer and recurrence risk

Background: Several retrospective studies report an improved overall (and possibly disease-free) survival of women who become pregnant following breast cancer diagnosis compared to women who choose not to or are unable to become pregnant. The objective of the current study is to evaluate associations with breast cancer biologic and stage characteristics from the baseline tumor with different recurrence outcomes in women with and without a pregnancy subsequent to their cancer diagnosis. Methods: From a population-based cohort study of all women aged 20-44 diagnosed with invasive breast cancer in the three county Seattle-Puget Sound metropolitan area, we conducted a secondary recontact interview. Recontact information included cancer recurrence and obstetric history, including all pregnancies occurring after breast cancer diagnosis. Univariate associations were evaluated using chi square. A time-to-event analysis was conducted, evaluating the relationship between pregnancy and recurrence, with consideration of stage and tumor type (triple negative tumor or not) as confounders. Results: At this interim, an approximately 70% response rate for the re-contact study was achieved, yielding data from 458 women overall. Excluding 8 women who were pregnant at the time of their breast cancer diagnosis, 450 were available for analysis. Of these, 13 (2.9%) became pregnant at least once after their breast cancer diagnosis. Among women with complete pathologic information available (n = 274), those with a pregnancy subsequent to their cancer diagnosis had triple negative tumor types more often than those who did not have a subsequent pregnancy (4/8, 50% vs. 44/266, 17%, p = 0.03). Tumor stage did not differ between women with and without a subsequent pregnancy. Overall, 30 total cancer recurrences were captured in the re-contacted cohort; none of these occurred among women with subsequent pregnancy (0/13, 0% vs. 30/437, 6.9% among women without subsequent pregnancy), p = 0.3. For 448/450 women with complete information on timing of recurrence, a time-to-event analysis adjusting for tumor type did not show a significant association between subsequent pregnancy and recurrence risk, p = 0.14 by Likelihood Ratio test. Conclusions: In this population, breast cancer recurrence risk was not increased among women with a pregnancy subsequent to their cancer diagnosis. Despite the more common triple negative tumor type among the group of women with subsequent pregnancy, none of these women experienced a cancer recurrence. Our study adds to a substantial literature suggesting that pregnancy after breast cancer does not appear to have a detrimental effect on disease recurrence. The relationship between tumor type and its potential influence on both decision-making regarding pregnancy and the biology of pregnancy as it relates to breast cancer recurrence merits further investigation. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P3-08-11.