Table 1.
Distribution of selected baseline characteristics among the breast cancer case patients and subcohort members without breast cancer*
| Variable | Case patients (n = 875) |
Subcohort members (n = 821)† |
P‡ |
|---|---|---|---|
| Median age, y (IQR) | 64.0 (59.0–69.0) | 63.0 (57.0–69.0) | .001 |
| Race/ethnicity, No. (%) | |||
| White | 766 (87.5) | 701 (85.4) | .402 |
| Black | 58 (6.6) | 55 (6.7) | |
| Hispanic | 25 (2.9) | 32 (3.9) | |
| Asian/other | 26 (3.0) | 33 (4.0) | |
| Highest education level, No. (%) | |||
| High school or less | 152 (17.4) | 167 (20.3) | .082 |
| Some college | 304 (34.7) | 303 (36.9) | |
| College and above | 409 (46.7) | 342 (41.7) | |
| Missing | 10 (1.1) | 9 (1.1) | |
| Age at menarche in y, No. (%) | |||
| ≤11 | 216 (24.7) | 185 (22.5) | .479 |
| 12–13 | 449 (51.3) | 444 (54.1) | |
| ≥14 | 205 (23.4) | 189 (23.0) | |
| Missing | 5 (0.6) | 3 (0.4) | |
| Age at menopause in y, No. (%) | |||
| ≤42 | 127 (14.5) | 180 (21.9) | < .001 |
| 43–48 | 189 (21.6) | 195 (23.8) | |
| 49–51 | 219 (25.0) | 182 (22.2) | |
| ≥52 | 260 (29.7) | 199 (24.2) | |
| Missing | 80 (9.1) | 65 (7.9) | |
| Years of menstrual cycling, No. (%) | |||
| ≤33 | 237 (27.1) | 287 (35.0) | .001 |
| 34–38 | 267 (30.5) | 252 (30.7) | |
| ≥39 | 289 (33.0) | 216 (26.3) | |
| Missing | 82 (9.37) | 66 (8.0) | |
| Parity, No. (%) | |||
| No live births | 120 (13.7) | 120 (14.6) | .586 |
| 1 | 63 (7.2) | 72 (8.8) | |
| 2–3 | 446 (51.0) | 402 (49.0) | |
| ≥4 | 241 (27.5) | 222 (27.0) | |
| Missing | 5 (0.6) | 5 (0.6) | |
| Age at first child’s birth in y, No. (%) | |||
| ≤19 | 83 (11.0) | 78 (11.1) | .002 |
| 20–24 | 288 (38.2) | 320 (45.7) | |
| 25–29 | 234 (31.0) | 170 (24.3) | |
| ≥30 | 79 (10.5) | 58 (8.3) | |
| Missing | 71 (9.4) | 75 (10.7) | |
| Ever use of oral contraceptives, No. (%) | 356 (40.7) | 337 (41.1) | .880 |
| Hormone therapy at baseline, No. (%) | |||
| Not using hormone therapy | 412 (47.1) | 447 (54.4) | .007 |
| Combined estrogen + progestin therapy | 239 (27.3) | 182 (22.2) | |
| Unopposed estrogen therapy | 224 (25.6) | 191 (23.3) | |
| Missing | 0 | 1 (0.1) | |
| Smoking status, No. (%) | |||
| Never | 419 (47.9) | 439 (53.5) | .005 |
| Former | 404 (46.2) | 320 (39.0) | |
| Current | 39 (4.5) | 52 (6.3) | |
| Missing | 13 (1.5) | 10 (1.2) | |
| Median alcohol consumption, servings per week (IQR) | 0.6 (0.0–3.8) | 0.4 (0.0–2.7) | .006 |
| NSAID use ≥ 2 wks, No. (%) | 371 (42.4) | 298 (36.3) | .010 |
| Median body mass index, kg/m2 (IQR) | 25.9 (23.2–30.3) | 26.2 (23.3–29.7) | .894 |
| Median physical activity, METs/ wk (IQR) | 10.5 (3.4–19.8) | 10.0 (3.8–20.0) | .784 |
| First-degree relative with breast cancer, No. (%) | 217 (24.8) | 150 (18.3) | .005 |
| History of benign breast disease, No. (%) | 329 (37.6) | 259 (31.6) | .009 |
| Estrogen receptor status, No. (%) | -- | ||
| Positive | 554 (63.3) | -- | |
| Negative | 253 (28.9) | -- | |
| Missing | 68 (7.8) | -- | |
| Median levels of analytes (IQR) | |||
| Leptin, pg/mL | 13950 (7433–25025) | 14406 (6974–24698) | .497 |
| Adiponectin, ng/mL | 28597 (20109–40085) | 29317 (20498–39929) | .571 |
| Resistin, ng/mL | 12.1 (9.7–15.1) | 12.3 (9.8–15.6) | .454 |
| CRP, μg/mL | 2.3 (1.0–4.7) | 1.9 (0.9–4.4) | .057 |
| IL-6, pg/mL | 1.4 (0.9–2.3) | 1.4 (0.9–2.2) | .794 |
| TNF-α, pg/mL | 2.5 (1.8–3.4) | 2.6 (1.8–3.6) | .756 |
| PAI-1, pg/mL | 14237 (9300–21076) | 14076 (8898–20726) | .409 |
| HGF, pg/mL | 611 (401–873) | 604 (404–855) | .588 |
| Insulin, µIU/mL | 5.7 (3.5–8.8) | 5.3 (3.3–8.5) | .196 |
| Estradiol, pg/mL§ | 11.9 (8.0–16.0) | 11.0 (7.0–16.0) | .025 |
* All statistical tests were two-sided. IQR = interquartile range; METs = metabolic equivalent tasks (defined as the caloric need per kilogram of body weight per hour of activity divided by the caloric need per kilogram of body weight per hour at rest); NSAID = nonsteroidal anti-inflammatory drug.
† Excludes women who developed breast cancer during follow-up.
‡ Missing are excluded for P value calculation.
§ Among women not using hormone therapy at baseline.