OBJECTIVE: To determine cancer incidence among Finnish women with 10 or more deliveries.
METHODS: Finnish women with at least 10 childbirths before December 31, 2010 (n=4,967) were identified from the Finnish Population Register and followed for cancer incidence through the Finnish Cancer Registry to the end of 2010. Cancer risks in this cohort were expressed as ratios between observed and expected numbers of cases (standardized incidence ratios), both drawn from the Finnish Cancer Registry, with 95% confidence intervals (CIs).
RESULTS: Total cancer incidence was markedly lower than in the reference population (656 cases, standardized incidence ratio 0.76, 95% CI 0.73–0.79). There was clearly less breast (0.44, 0.35–0.53), ovarian (0.49, 0.28–0.80), endometrial (0.31, 0.17–0.44), and basal cell skin cancer (0.72, 0.60–0.85) than in the reference population. The incidence of thyroid cancer (2.33, 1.59–3.29), lip cancer (2.87, 1.05–6.24), and uterine sarcoma (3.41, 1.47–6.72) was markedly increased.
CONCLUSION: Women with 10 or more deliveries show a decreased overall cancer incidence as a result of decreased risks of cancers of the ovary, endometrium, and breast and basal cell carcinoma of the skin. The increased risks were observed in thyroid cancer and some rare cancer types.
LEVEL OF EVIDENCE: II