BMC Cancer 2008, 8:90 http://www.biomedcentral.com/1471-2407/8/90 control pairs. For 83 pairs, we adjusted the risks for poten- tial ovarian cancer risk factors, referred to as adjusted odds ratios (ORadj), by including age at menarche, age at first live birth, parity (0, 1, 2, 3, 4, 4+ children), lifetime cumu- lative months of breastfeeding (≤12 and >12 months), oral contraceptive (OC) use (<5 and ≥5 years), hormone replacement therapy (HRT) use (never, ever), smoking (<4 and ≥4 pack-years) and body mass index (BMI) (at age of breast cancer diagnosis for cases and at corresponding age for controls) in the penalized-likelihood logistic regression model [17]. Age comparisons among carriers of different genotypes were performed using the Mann-Whitney U-test. Exact 95% confidence intervals were calculated for binomial probabilities. The statistical analyses were done using the software package R, version 2.3.1 [18] with packages "sur- vival", version 2.26, and "logistf", version 1.06. In order to account for a potential bias due to the presence of rela- tives, we performed a second analysis using only unre- lated study subjects. After exclusion of the pairs with Table 1: Comparison of ovarian cancer cases and matched controls relatives, ORcrude were calculated for 104 pairs and ORadj for 69 pairs. Two-sided p values of 0.05 or less were con- sidered as statistically significant. Results Description of the study participants A total of 254 BRCA1 mutation carriers including 127 ovarian cancer cases and 127 unaffected controls were included in this study. All mutation carriers were selected from families with at least one ovarian cancer diagnosed at any age or with multiple cases of breast and ovarian cancer. Controls were matched to cases by year of birth and BRCA1 mutation and were similar to cases with respect to potential ovarian cancer risk factors including year of birth, age at first live birth, age at menarche, BMI, parity, breastfeeding, and smoking. In contrast, OC use of 5 years and more and HRT use were less frequently reported by ovarian cancer cases than by controls (0 cases, 8 controls; 2 cases and 11 controls, respectively; Table 1). These differences were not considered relevant because of the small number of individuals. Characteristic Year of birth (median) Age of 1st live birth (median) Age at menarche (median) BMI (median) Age (median) Parity 0 1 2 3 4 >4 Breastfeedingc ≤ 12 months >12 months OC use <5 years ≥ 5 years HRT Never Ever Smokingd <4 pack-years ≥ 4 pack-years BRCA1 mutation 5382insC 300T>G 4154delA Cases (n = 83) n (%) 1953 (range 1928–1971) 22 (range 16–38) 14 (range 10–17) 25 (range 19–38) 45a (range 25–71) 7 (8) 11 (13) 43 (52) 13 (16) 7 (8) 2 (3) 20 (26) 56 (74) 83 (100) 0 (0) 81 (97) 2 (3) 56 (67) 24 (29) 61 (74) 16 (19) 6 (7) BMI: body mass index; OC: oral contraceptive; HRT: hormone replacement therapy. a Age at diagnosis of ovarian cancer. b Age at the time of matching. c Nulliparous women were excluded. d Missing information on smoking status from three cases. Controls (n = 83) n (%) 1953 (range 1929–1971) 23 (range 17–35) 14 (range 9–18) 25 (range 17–44) 49b (range 31–73) 7 (8) 12 (14) 41 (50) 17 (20) 4 (5) 2 (3) 23 (30) 53 (70) 75 (90) 8 (10) 72 (87) 11 (13) 52 (63) 31 (37) 61 (74) 16 (19) 6 (7) Page 3 of 5 (page number not for citation purposes)