A recent systematic review and meta-analysis of the association between body weight or body mass index (BMI) and ovarian cancer concluded that there is a modest association between high adult BMI and epithelial ovarian cancer.1 However, most studies reviewed had combined the histological subtypes of ovarian cancer despite some known differences in risk factors,2–4 with relatively few studies reporting results for the different histological subtypes of ovarian cancer.5–12 Obesity is a well-established risk factor for endometrial cancer13 and as histologically similar endometrioid tumors also occur in the ovary,14 it could be hypothesized that obesity would also be a strong risk factor for this subtype of ovarian cancer. However, while 2 previous studies9, 15 observed an increased prevalence of overweight amongst women with the endometrioid subtype of ovarian cancer, others have failed to confirm this finding.6–8
Since obesity early in life has been positively associated with other hormone-dependent cancers, and inversely associated with premenopausal breast cancer,16, 17 and adult weight gain has been positively associated with of breast18 and endometrial cancer,19 it is relevant to evaluate the association between BMI in early adulthood, weight gain and risk of ovarian cancer. Only one previous study12 has examined the possible links between BMI in early adulthood by subtype of ovarian cancer, but analysis was limited to the most common serous subtype. Three case-control studies5, 20, 21 and 3 cohort studies12, 22, 23 have examined the association between weight gain from early adulthood and risk of ovarian cancer; however, only one study5 examined the association for the histological subtypes of ovarian cancer; they observed an increased risk of the serous and mucinous subtypes among nulliparous women only.
Three7, 8, 21 of 4 studies7, 8, 12, 21 that have examined the risks of ovarian cancer associated with obesity separately for pre- and postmenopausal women have reported higher risk estimates associated with high BMI among premenopausal women. In contrast high BMI has consistently been shown to be positively associated with post- but not premenopausal breast cancer,24, 25 and it has been hypothesized that this increased risk of breast cancer in postmenopausal women is mediated through oestrogenic effects.26 The relationship between BMI and menopausal status has not been examined for the different histological subtypes of ovarian cancer.
In this report, we describe a detailed analysis of self-reported body size during adult life in relation to risk of the major histological subtypes of ovarian cancer using data collected from an Australia-wide, population-based case-control study. We also examined these associations by menopausal status, parity and use of hormone replacement therapy (HRT) (postmenopausal women). We conducted analyses for all invasive serous tumors combined, and then separately by cancer site, ovary and fallopian tube combined, and peritoneum, because previous research suggested that serous cancers of the peritoneum may differ aetiologically from serous cancers of the ovary and fallopian tube.27