Table 1.
Characteristics of second primary contralateral breast cancer case subjects and control subjects*
| Characteristic | Contralateral breast cancer case subjects (n = 351) | Control subjects (n = 662) | P† |
| No. (%) | No. (%) | ||
| Data obtained through the cancer registry | |||
| Age at first breast cancer diagnosis, y | |||
| 40–49 | 69 (19.7) | 122 (18.4) | |
| 50–59 | 88 (25.1) | 175 (26.4) | |
| 60–69 | 108 (30.8) | 203 (30.7) | |
| 70–79 | 86 (24.5) | 162 (24.5) | NA |
| Year of first breast cancer diagnosis | |||
| 1990–1994 | 153 (43.6) | 289 (43.7) | |
| 1995–1999 | 143 (40.7) | 261 (39.4) | |
| 2000–2005 | 55 (15.7) | 112 (16.9) | NA |
| AJCC stage‡ | |||
| I | 228 (65.0) | 447 (67.5) | |
| II | 107 (30.5) | 186 (28.1) | |
| III | 16 (4.6) | 29 (4.4) | NA |
| County of residence from first breast cancer diagnosis to reference date | |||
| King | 171 (48.7) | 338 (51.1) | |
| Pierce | 83 (23.6) | 153 (23.1) | |
| Snohomish | 67 (19.1) | 118 (17.8) | |
| Thurston | 30 (8.5) | 53 (8.0) | NA |
| Progesterone receptor status of first breast cancer | |||
| Negative | 44 (12.5) | 95 (14.4) | |
| Positive | 307 (87.5) | 567 (85.6) | .49 |
| Vital status at enrollment | |||
| Alive | 260 (74.1) | 532 (80.4) | |
| Deceased | 91 (25.9) | 130 (19.6) | .005 |
| Data obtained primarily by medical record review | |||
| Height at first breast cancer diagnosis, in | |||
| <62 | 42 (12.3) | 94 (14.9) | |
| 62 to <64 | 120 (35.1) | 247 (39.3) | |
| 64 to <66 | 96 (28.1) | 160 (25.4) | |
| ≥66 | 84 (24.6) | 128 (20.3) | |
| Missing | 9 | 33 | .19 |
| Weight at first breast cancer diagnosis§, kg | |||
| <61 | 63 (18.2) | 160 (24.3) | |
| 61 to <69 | 81 (23.4) | 171 (26.0) | |
| 69 to <82 | 85 (24.6) | 158 (24.0) | |
| ≥82 | 117 (33.8) | 169 (25.7) | |
| Missing | 5 | 4 | .02 |
| BMI at first breast cancer diagnosis§, kg/m2 | |||
| <25 | 123 (35.8) | 286 (43.7) | |
| 25 to <30 | 115 (33.4) | 196 (30.0) | |
| ≥30 | 106 (30.8) | 172 (26.3) | |
| Missing | 7 | 8 | .04 |
| Osteoporosis or osteopenia diagnosis before reference date | |||
| No | 255 (73.5) | 465 (70.3) | |
| Yes | 92 (26.5) | 196 (29.7) | |
| Missing | 4 | 1 | .28 |
| No. of surveillance mammograms from first breast cancer diagnosis to reference date§ | |||
| 0 | 5 (1.4) | 54 (8.3) | |
| 1–4 | 159 (45.8) | 299 (45.7) | |
| 5–9 | 152 (43.8) | 254 (38.8) | |
| 10–14 | 29 (8.4) | 42 (6.4) | |
| ≥15 | 2 (0.6) | 5 (0.7) | |
| Missing | 4 | 8 | <.001 |
| Treatment with aromatase inhibitors, mo | |||
| None | 330 (94.6) | 598 (90.6) | |
| 1–5 | 7 (2.0) | 16 (2.4) | |
| ≥6 | 12 (3.4) | 46 (7.0) | |
| Missing | 2 | 2 | .02 |
| Treatment with tamoxifen, mo | |||
| None | 139 (39.7) | 212 (32.3) | |
| 1–5 | 30 (8.6) | 45 (6.8) | |
| ≥6 | 181 (51.7) | 400 (60.9) | |
| Missing | 1 | 5 | .01 |
| Treatment with chemotherapy§ | |||
| No | 261 (74.8) | 485 (73.4) | |
| Yes | 88 (25.2) | 176 (26.6) | |
| Missing | 2 | 1 | .45 |
| Treatment with radiation§ | |||
| No | 122 (34.8) | 226 (34.2) | |
| Yes | 229 (65.2) | 435 (65.8) | |
| Missing | 0 | 1 | .97 |
| Data obtained primarily by telephone interview | |||
| Race/ethnicity‖ | |||
| Non-Hispanic white | 322 (92.3) | 609 (92.3) | |
| Black | 9 (2.6) | 18 (2.7) | |
| Asian or Pacific Islander | 10 (2.9) | 21 (3.2) | |
| Native American | 5 (1.4) | 9 (1.4) | |
| Hispanic white | 3 (0.9) | 3 (0.5) | |
| Missing | 2 | 2 | NA |
| No. of full-term pregnancies by first breast cancer diagnosis‖ | |||
| 0 | 56 (16.4) | 102 (15.7) | |
| 1 | 43 (12.6) | 81 (12.5) | |
| 2 | 106 (31.1) | 193 (29.7) | |
| 3 | 67 (19.6) | 147 (22.7) | |
| ≥4 | 69 (20.2) | 126 (19.4) | |
| Missing | 10 | 13 | .76 |
| Menopausal status at first breast cancer diagnosis | |||
| Natural menopause | 129 (52.9) | 261 (51.9) | |
| Premenopause | 45 (18.4) | 86 (17.1) | |
| Induced menopause | 30 (12.3) | 63 (12.5) | |
| Simple hysterectomy | 40 (16.4) | 93 (18.5) | |
| Missing | 107 | 159 | .90 |
| Average weekly alcohol consumption in the 5 years before first breast cancer diagnosis | |||
| None | 105 (42.0) | 226 (43.5) | |
| <3 drinks | 74 (29.6) | 150 (28.9) | |
| ≥3 drinks | 71 (28.4) | 143 (27.6) | |
| Missing | 101 | 143 | .55 |
| Smoking status at first breast cancer diagnosis | |||
| Never smoker | 120 (47.6) | 274 (52.5) | |
| Former smoker | 49 (19.4) | 77 (14.8) | |
| Current smoker | 83 (32.9) | 171 (32.8) | |
| Missing | 99 | 140 | .16 |
| Use of unopposed estrogen or estrogen and progestin pill or patch for ≥6 mo before first breast cancer diagnosis‖ | |||
| Ever | 161 (49.4) | 319 (51.9) | |
| Never | 165 (50.6) | 296 (48.1) | |
| Missing | 25 | 47 | .41 |
| First-degree family history of breast cancer at reference date‖ | |||
| No | 231 (70.9) | 467 (74.2) | |
| Yes | 95 (29.1) | 162 (25.8) | |
| Missing | 25 | 33 | .35 |
For each matched case–control set, the reference date was defined at the date on which the case subject was diagnosed with a second primary contralateral breast cancer. AJCC = American Joint Committee on Cancer; BMI = body mass index.
Likelihood ratio test P value comparing conditional logistic regression models with and without adjustment for the given characteristic. Models are implicitly adjusted for matching factors (age at and year of diagnosis with first primary breast cancer, Surveillance, Epidemiology and End Results historic stage [localized vs regional] of the first primary breast cancer, county of residence, and race/ethnicity).
AJCC stage derivations for diagnoses made before 2004 were made according to version 1.1 of the SEER Program: Comparative Staging Guide for Cancer (18); subsequent diagnoses were staged according to the 10th edition of the North American Association for Central Cancer Registries Standards for Cancer Registries Volume II (19).
Supplemented by interview.
Supplemented by medical record review.