Table 1.
Distribution of background factors in postmenopausal women diagnosed with breast cancer in relation to age at menarche
| Age at menarche, years | P valuea | ||||
| ≤ 11 | > 11 and ≤13 | > 13 and ≤14 | > 14 | ||
| Column frequency, number (percentage) | |||||
| Total number of cases (n = 2,640) | 167 | 989 | 698 | 542 | |
| Background factors | |||||
| Menstrual cycle length, days | |||||
| ≤27.5 | 35 (30) | 183 (26) | 125 (26) | 93 (26) | |
| 28 | 64 (55) | 392 (55) | 258 (54) | 191 (54) | |
| > 28 | 17 (15) | 136 (19) | 96 (20) | 71 (20) | 0.877 |
| Irregular menstruation | |||||
| No | 159 (96) | 39 (4) | 18 (3) | 518 (98) | |
| Yes | 7 (4) | 940 (96) | 672 (97) | 13 (2) | 0.246 |
| Age at first birth, years | |||||
| < 25 | 73 (51) | 418 (50) | 268 (45) | 226 (49) | |
| ≥25 and < 30 | 44 (31) | 281 (34) | 200 (34) | 149 (32) | |
| ≥30 | 27 (19) | 136 (16) | 129 (21) | 86 (19) | 0.240 |
| Parity | |||||
| 0 | 23 (14) | 154 (16) | 101 (14) | 81 (15) | |
| 1 | 30 (18) | 215 (21) | 154 (22) | 105 (19) | |
| 2 | 68 (41) | 362 (37) | 269 (39) | 215 (40) | |
| 3+ | 46 (28) | 258 (26) | 174 (25) | 141 (26) | 0.893 |
| Pregnancy terminated < 6 months, nulliparous | |||||
| No | 7 (88) | 15 (38) | 18 (49) | 9 (45) | |
| Yes | 1 (12) | 25 (62) | 19 (51) | 11 (55) | 0.079 |
| Pregnancy terminated < 6 months, parous | |||||
| No | 100 (71) | 631 (76) | 431 (73) | 363 (79) | |
| Yes | 40 (29) | 197 (24) | 160 (27) | 95 (21) | 0.069 |
| Age at menopause, yearsb | |||||
| < 50 | 45 (31) | 261 (31) | 198 (34) | 133 (28) | |
| 50–55 | 86 (59) | 520 (62) | 344 (58) | 299 (63) | |
| > 55 | 14 (10) | 55 (7) | 47 (8) | 43 (9) | 0.312 |
| Ever use of MHTc | |||||
| No | 105 (63) | 646 (66) | 483 (69) | 370 (68) | |
| Yes | 61 (37) | 340 (34) | 215 (31) | 171 (32) | 0.258 |
| MHT use by general type | |||||
| Exclusive estrogen use | 14 (9) | 67 (7) | 54 (8) | 39 (8) | |
| Estrogen-progestin combined use | 39 (25) | 233 (25) | 142 (21) | 111 (21) | 0.566 |
| Diagnosed via mammographic screening | |||||
| Screening | 102 (61) | 546 (56) | 399 (58) | 301 (57) | |
| Other | 64 (39) | 436 (44) | 288 (42) | 228 (43) | 0.484 |
| Deceased at end of 5-year follow-up | 27 (16) | 134 (14) | 101 (15) | 74 (14) | 0.802 |
| Breast cancer deaths at end of 5-year follow-up (total = 264) | 23 (14) | 89 (9) | 71 (10) | 46 (8) | 0.186 |
aPearson chi-square tests of association between groups. bAmong women with a natural known menopause. cMenopausal hormone therapy includes all treatments: exclusive estrogens, exclusive progestins, and combined estrogen-progestin therapy.