Risk of female-specific cancers according to obesity and menopausal status in 2•7 million Korean women: Similar trends between Korean and Western women.
Background
Studies examining the relationship between obesity and female-specific cancers have been mainly conducted in Western populations. We aimed to investigate the risk of female-specific cancers according to obesity and menopausal status using a nationwide cohort in Korea.


Methods
We identified 2,708,938 women from the National Health Insurance Service cohort, and obtained baseline body mass index (BMI), waist circumference (WC), and other healthcare data, measured and collected during a health examinations and cancer-screening survey. By setting a normal weight/WC group (BMI, 18•5-22•9 kg/m2 or WC, 80•0-84•9 cm) as the reference, we conducted multivariate analyses using the Cox proportional hazard model to estimate adjusted hazard ratios (aHRs) and 95% confidence intervals (95% CIs) for each cancer.


Findings
The total follow-up duration was 22389854•63 person-years. In post-menopausal women, the risk of breast, endometrial, and ovarian cancers significantly increased as the BMI classification level increased from normal to class II obesity (aHRs [95% CIs], 1•49 [1•38-1.61], 2•11 [1•81-2•46], and 1•38 [1•20-1•58], respectively). The risk of breast and endometrial cancers also increased as the WC classification increased from < 75•0 to ≥ 95•0 cm. With a WC of 80•0-84•9 cm as the reference, the lowest risk of breast and endometrial cancers was observed in WC < 75•0 cm (aHRs [95% CIs], 0•85 [0•81-0•89] and 0•75 [0•67-0•84], respectively) while the highest risk was observed in WC ≥ 95•0 cm (aHRs [95% CIs], 1•19 [1•10-1•29] and 1•56 [1•33-1•82], respectively). In pre-menopausal women, the risk of breast cancer significantly decreased in those with class I and II obesity compared to those with normal BMI (aHRs [95% CIs], 0•96 [0•92-0•999] and 0•89 [0•81-0•97], respectively), whereas the trends of endometrial and ovarian cancer incidence in pre-menopausal women were similar to those observed in post-menopausal women. For cervical cancer, only class II obesity was significantly associated with increased risks in both post-menopausal and pre-menopausal women (aHRs [95% CIs], 1•18 [1•01-1•39] and 1•27 [1•02-1•57], respectively).


Interpretation
In this large population-based cohort study in Korean women, we observed that the impact of obesity on the development of female-specific cancers differs according to the malignancy type and menopausal status. Similar trends were observed between Korean and Western women.


Funding
The Korea Health Industry Development Institute (no. HI16C2037).
['Park|In Sil|IS|', 'Kim|Se Ik|SI|', 'Han|Youngjin|Y|', 'Yoo|Juhwan|J|', 'Seol|Aeran|A|', 'Jo|HyunA|H|', 'Lee|Juwon|J|', 'Wang|Wenyu|W|', 'Han|Kyungdo|K|', 'Song|Yong Sang|YS|']
Obesity Menopause Body mass index Waist circumference Ovarian cancer Endometrial cancer Breast cancer Incidence Cervical cancer