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


Sun, Xuezheng; Nichols, Hazel B.; Tse, Chiu-Kit J.; Bell, Mary Elizabeth; Robinson, Whitney R.; Sherman, Mark E.; Olshan, Andrew F.; & Troester, Melissa A. (2016). Association of Parity and Time since Last Birth with Breast Cancer Prognosis by Intrinsic Subtype. Cancer Epidemiology, Biomarkers & Prevention, 25(1), 60-67. PMCID: PMC4727837


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 has 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 (BC)-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 BC-specific mortality, independent of age, race, and selected socioeconomic factors (parity, reference=nulliparous, adjusted hazard ratio [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 biological effects of parity and birth recency may extend from etiology to tumor promotion and progression.


Reference Type

Journal Article

Year Published


Journal Title

Cancer Epidemiology, Biomarkers & Prevention


Sun, Xuezheng
Nichols, Hazel B.
Tse, Chiu-Kit J.
Bell, Mary Elizabeth
Robinson, Whitney R.
Sherman, Mark E.
Olshan, Andrew F.
Troester, Melissa A.