Parity and age at first childbirth in relation to the risk of different breast cancer subgroups

Abstract

The aim of the present study was to examine parity and age at first childbirth, in relation to the risk of specific breast cancer subgroups. A prospective cohort, The Malmö Diet and Cancer Study, including 17,035 women were followed with linkage to Swedish Cancer Registry until December 31, 2004. A total of 622 incident breast cancers were diagnosed during follow‐up and were evaluated regarding invasiveness, tumour size, axillary lymph node status, Nottingham grade, tumour proliferation (Ki67), HER2, cyclin D1 and p27. The tumours were also examined for WHO type and hormone receptor status. Nulliparity was associated with an overall increased risk of breast cancer, although not statistically significant (the relative risk was 1.39 with a 95% confidence interval of 0.92–2.08). Nulliparity was also associated with large tumours (>20 mm) (1.89: 0.91–3.91), high Ki67 levels (1.95: 0.93–4.10), high cyclin D1 levels (2.15: 0.88–5.27), grade III (2.93: 1.29–6.64) and HER2 positive tumours (3.24: 1.02–10.25). High parity was not statistically significantly associated with any specific breast cancer subgroup. Older age at first childbirth (>30) was associated with a slightly increased risk of breast cancer (1.39: 0.94–2.07). There was a statistically significant association between late first childbirth and lobular type (2.51: 1.01–6.28), grade III tumours (2.67: 1.19–6.02), high levels of cyclin D1 (2.69: 1.18–6.12) and low levels of p27 (2.23: 1.15–4.35). We conclude that nulliparity and late first childbirth are associated with relatively more aggressive breast cancer subgroups. © 2009 UICC

Factors influencing the association between CYP17 T34C polymorphism and the risk of breast cancer: meta-regression and subgroup analysis

“…In consequence, when tested separately, some of the subgroups will fail to show the statistically significant association that was shown in the main population; at the same time, the conclusion can be misleading. For example, the present study showed that an increased risk of breast cancer in the parous women with C allele, which was so contradictory to the commonly agreed linkage between null parity and increased breast cancer [64]. Low statistical power of studies (less than 5.2% in the subgroup of pre-menopausal women with parity) requires large population-based studies with sufficient sample size, to reduce the occurrence of false positives (type II errors), and to provide convincing evidence for accurate and reliable statistical judgments [38].…”

The association of reproductive factors and breastfeeding with long term survival from breast cancer

“…In a recent cohort study of postmenopausal women with breast cancer in Sweden [25], the investigators found that late age at first pregnancy and nulliparity were associated with increased tumor expression of proteins that indicate relatively aggressive tumor behavior. The results of that study appear to support our findings that patients with late age at first birth may tend to develop more aggressive cancers, and therefore have relatively poorer survival.…”

Age at first childbirth and oral contraceptive use are associated with risk of androgen receptor-negative breast cancer: the Malmö Diet and Cancer Cohort

“…Ma et al hypothesized that the protective effect of parity could be explained by reduced circulating hormone levels, increased levels of sex hormone binding globulin SHBG, or by increasing the breast epithelium differentiation to a less susceptible state concerning the effects of estrogen and progestin (24). Previous results from the MDCS have suggested that advanced age at first childbirth and parity correlate to more aggressive breast cancer subtypes (39), which is in agreement with the current findings of an association between advanced age at first childbirth and risk of AR -breast cancer. A recently published case study, showed increasing frequency of TNBC among women with an older age at first child birth.…”