P1-08-09: Increased Mortality in Swedish Women Diagnosed with Breast Cancer during and Shortly after Pregnancy.

Abstract

Abstract Background: The incidence of pregnancy-associated breast cancer (PABC), i.e. breast cancer diagnosed during pregnancy or within two years after delivery, is increasing in Sweden. Results from epidemiological studies suggest that women with PABC have worse prognosis than women of same age and no recent birth. We studied the mortality in women with PABC, compared to women with a diagnosis of breast cancer not close to pregnancy, and in relation to when the PABC diagnosis occurred (during pregnancy, different postpartum periods). We also studied whether mortality varied over time since diagnosis. Materials and Methods: We used data from the Swedish National Cancer Register to identify all women diagnosed with breast cancer between ages 15–44 years during 1963–2002 (n=15,729). The study cohort was linked to the Multi-Generation Register to obtain information on childbirths and when they occurred. We estimated mortality rates among women with and without PABC, and subdivided by time of detection among PABC patients (PABC during pregnancy, or during months 1–3, 4–6, 7–12, 13–18, 19–24 after delivery). Hazard ratios (HR) with 95% confidence intervals (CI) were estimated using the novel method of flexible parametric survival models. These models use splines to model the baseline hazard rate, and are able to pick up more subtle time-dependent effects than the more commonly used piecewise splitting of the timescale (for example in Poisson regression). Results: Women with PABC had higher mortality than women diagnosed at the same age and calendar period and with no recent birth. In women with PABC (n=1,110), 46% died during follow-up, compared to 34% of the non-PABC patients (n=14,611). The mortality in both groups peaked at around two years after diagnosis, with the highest peak occurring in women diagnosed 4–6 months after delivery (HR=3.8, 95% CI 2.4−5.9). Also, among women diagnosed during pregnancy the mortality was higher compared to women diagnosed further away from delivery. An increased mortality among women with PABC remained up to 10 years after diagnosis. Discussion: Women with PABC had a poorer prognosis compared to women with breast cancer and no recent birth. The worse prognosis may be due to diagnostic delays or tumour promoting hormonal boosts or changes in the tumour micro-environment post-partum. Taken together, our findings indicate that women with PABC represent a high-risk group of young breast cancer patients that may require special management. Also, by applying novel statistical methods we were able to detect time dependent effects in that the elevated mortality associated with PABC varied by timing of diagnosis and time since diagnosis. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-08-09.