Association of Parity and Time since Last Birth with Breast Cancer Prognosis by Intrinsic Subtype.

BACKGROUND

Parity and time since last birth influence breast cancer risk and vary by intrinsic tumor subtype, but the independent effects of these factors on prognosis have received limited attention.

METHODS

Study participants were 1,140 invasive breast cancer patients from phases I and II of the population-based Carolina Breast Cancer Study, with tissue blocks available for subtyping using immunohistochemical markers. Breast cancer risk factors, including pregnancy history, were collected via in-person interviews administered shortly after diagnosis. Vital status was determined using the National Death Index. The association of parity and birth recency with breast cancer-specific and overall survival was assessed using Cox proportional hazards models.

RESULTS

During follow-up (median = 13.5 years), 450 patients died, 61% due to breast cancer (n = 276). High parity (3+ births) and recent birth (<5 years before diagnosis) were positively associated with breast cancer-specific mortality, independent of age, race, and selected socioeconomic factors [parity, reference = nulliparous, adjusted HR = 1.76; 95% confidence interval (CI) = 1.13-2.73; birth recency, reference = 10+ years, adjusted HR = 1.29; 95% CI, 0.79-2.11]. The associations were stronger among patients with luminal tumors and those surviving longer than 5 years.

CONCLUSIONS

Parity and recent birth are associated with worse survival among breast cancer patients, particularly among luminal breast cancers and long-term survivors.

IMPACT

The biologic effects of parity and birth recency may extend from etiology to tumor promotion and progression.