Table 1.
Melbourne Collaborative Cohort Study participant characteristics
| Characteristics | Cases of BC (n = 408) | Subcohort (n = 2783) | Whole cohort (n= 12 673) |
|---|---|---|---|
| Mean age (SD), y | 63.0 (6.9) | 63.6 (7.2) | 63.5 (7.2) |
| Mean height (SD), cm | 161.8 (6.2) | 161.1 (6.5) | 161.0 (6.6) |
| Mean weight (SD), kg | 73.0 (13.3) | 70.6 (13.5) | 70.8 (13.6) |
| Mean BMI (SD), kg/m2 | 27.9 (5.3) | 27.2 (5.2) | 27.4 (5.3) |
| Mean alcohol intake (SD), ethanol g/day | 8.6 (11.1) | 8.1 (11.4) | 8.0 (11.5) |
| Mean menarche age (SD), y | 12.8 (1.5) | 13.0 (1.6) | 13.0 (1.6) |
| Mean No. of live births (SD) | 2.3 (1.5) | 2.4 (1.5) | 2.4 (1.5) |
| Mean age at first birth (SD), y | 25.5 (4.7) | 25.2 (4.5) | 25.2 (4.6) |
| Mean age of menopause (SD), ya | 50.1 (5.1) | 49.7 (5.0) | 49.6 (5.0) |
| Mean incidence of breast cancerb per 1000 person-years (95% CI) | — | 1.17 (0.96 to 1.43) | 1.13 (1.02 to 1.24) |
| Oral contraceptive use, No. (%) | |||
| Never | 110 (27.0) | 830 (29.8) | 3766 (29.7) |
| Former | 296 (72.5) | 1937 (69.6) | 8858 (69.9) |
| Current | 2 (0.5) | 12 (0.4) | 37 (0.3) |
| Missing | — | 4 (0.1) | 12 (0.1) |
| Menopausal status,c No. (%) | |||
| Premenopausal | 344 (84.3) | 7 (0.3) | 37 (0.3) |
| Postmenopausal | 64 (15.7) | 2425 (87.1) | 11 025 (87.0) |
| Missing | — | 1 (0.0) | 3 (0.0) |
| Unable to determine | — | 350 (12.6) | 1608 (12.7) |
| Menopausal hormone therapy use,d No. (%) | |||
| Never | 184 (45.1) | 1424 (51.2) | 6524 (51.5) |
| Former | 200 (49.0) | 695 (25.0) | 3101 (24.5) |
| Current estrogen | 8 (2.0) | 32 (1.1) | 151 (1.2) |
| Current other hormone replacement therapy | 61 (15.0) | 222 (8.0) | 939 (7.4) |
| Current user but missing type | 20 (4.9) | 144 (5.2) | 680 (5.4) |
| Missing | 35 (8.6) | 266 (9.6) | 1278 (10.1) |
| Family history of breast cancer (first or second degree), No. (%) | |||
| No | 292 (71.6) | 2185 (78.5) | 9925 (78.3) |
| Yes | 116 (28.4) | 598 (21.5) | 2748 (21.7) |
| Mean PRS distribution (SD) | |||
| IBIS | 0.12 (0.64) | −0.12 (0.62) | — |
| BOADICEA | 0.50 (1.05) | 0.09 (1.02) | — |
Women whose reason for periods stopping were due to having had a natural menopause or a bilateral oophorectomy. — = not applicable; BC = breast cancer; BOADICEA = Breast and Ovarian Analysis of Disease Incidence and Carrier Estimation Algorithm model (version 5.0.0); IBIS = International Breast Cancer Intervention Study model (version 8 b); PRS = polygenic risk score based on 313 single nucleotide polymorphisms associated with breast cancer.
Standardized incidence rate.
Postmenopausal is defined as had menstrual period in last 12 months and currently using hormone replacement therapy (or missing) and aged at least 55 years; or no menstrual period in last 12 months (or missing) and periods stopped naturally; or no menstrual period in last 12 months (or missing) and periods stopped because both ovaries were removed; or no menstrual period in last 12 months (or missing) and periods stopped because of hysterectomy or other reason (or missing) and aged at least 55 years.
Type of hormone replacement therapy based on assumption of estrogen for those who have had a hysterectomy and combined estrogen and progesterone for those on hormone replacement therapy but have not had a hysterectomy.