Population attributable risks of modifiable reproductive factors for breast and ovarian cancers in Korea

open access

(abstract) Background

Breast and ovarian cancers are predominant female cancers with increasing prevalence. The purpose of this study was to estimate the population attributable risks (PARs) of breast and ovarian cancer occurrence based on the relative risks (RRs) of modifiable reproductive factors and population-specific exposure prevalence.

(abstract) Results

The summary PARs for modifiable reproductive factors were 16.7 % (95 % CI 15.8–17.6) for breast cancer (2404 cases) and 81.9 % (95 % CI 55.0–100.0) for ovarian cancer (1579 cases). The modifiable reproductive factors included pregnancy/age at first birth (8.0 %), total period of breastfeeding (3.1 %), oral contraceptive use (5.3 %), and hormone replacement therapy use (0.3 %) for breast cancer and included breastfeeding experience (2.9 %), pregnancy (1.2 %), tubal ligation (24.5 %), and oral contraceptive use (53.3 %) for ovarian cancer.

 

Meta-analysis for estimation of risk for breast and ovarian cancers

To obtain the pooled relative risks (RRs) for the selected risk factors, we conducted a meta-analysis of the results of large-scale, case–control studies in Korea (SeBCS for breast cancer and Ko-Eve for ovarian cancer) and the results from other previous studies. For breast cancer analysis, because the SeBCS included large numbers of cases and matched controls, we restricted the data selection to studies conducted in Korea and did not restrict the study design to reflect Korean risk estimates. For ovarian cancer analysis, given that the Ko-Eve is the only study conducted in Korea, and includes a limited number of cases, we included data from international studies to perform a meta-analysis with Ko-EVE results to obtain stable risk estimates.

The priority for inclusion of international data was meta-analysis or pooled analysis data. In cases where studies were not available, we included cohort study results. In cases where we could not obtain RR or the raw data necessary for calculating a RR estimate, the data were excluded from the meta-analysis.

Conclusions

In summary, the results of this study represent a systematic assessment of breast and ovarian cancer risks and the proportion of the risk associated with modifiable reproductive factors. A total of 16.7 % of breast cancer cases (2404 cases) and 81.9 % of ovarian cancer cases (1579 cases) in Korea among female individuals 20 years of age in 2010 were attributable to modifiable reproductive factors. Since breast and ovarian cancers are the most prevalent female cancers, and are showing a trend to higher prevalence, appropriate control of preventable or modifiable risk factors is an important strategy for reduction of the female cancer burden in Korea. Combining the current Korean family planning policy of childbirth encouragement with cancer control strategies that affect modifiable reproductive factors may help achieve reductions in breast and ovarian cancer incidences.