Some registry-based and population-based studies have suggested that high parity could be an adverse prognostic factor in luminal breast cancer, although the definition of breast cancer subtypes has been varied and prospective studies are lacking.
We report long-term follow-up (median 8.5 years) from prospectively collected single-institution material of early breast cancers. The patients (n = 612) were treated with modern treatment modalities in a Finnish university hospital clinic and clinicopathological surrogates of intrinsic subtypes were updated to match with the ESMO 2015 Early Breast Cancer Clinical Practice Guidelines. Long-term outcomes were recorded and special emphasis was given to exact reproductive factor anamnesis as a potential prognostic factor.
Ten-year breast cancer-specific survival (BCSS) in this real-life prospective population was 91.4% in the whole cohort. The longest ten-year BCSS was observed in luminal A-like cancers (97.6%) and the worst in luminal B-like (HER2-positive) subgroup (80.6%). Having five or more deliveries associated with dismal BCSS (univariate p = 0.0015). When subtypes were assessed separately in multivariate analysis, this association remained significant only in luminal B-like (HER2-negative) cancers (HR 2.64; 95% CI 1.05-6.65; p = 0.04) when tumor size and nodal status were also included to the analysis. Having 5 or more deliveries also associated with node positivity in the whole cohort (p = 0.0016), but not with different subtypes.
This is the first prospectively collected study with the modern definition of breast cancer subtypes and contemporary treatments to assess parity as a breast cancer prognostic factor. Our results suggest that high parity is an adverse prognostic factor, but only in luminal B-like (HER2-negative) subtype. The biological effects of parity seem extend to later breast cancer and its metastasis in estrogen dependent, rapidly proliferating breast cancers.
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All authors have declared no conflicts of interest.