Table 3.
Treatment equation models*
| Covariate† | BCS (N = 994) |
Radiation therapy among those having BCS (N = 611) |
||
| OR (95% CI) | P | OR (95% CI) | P | |
| Year | 1.61 (1.26 to 2.06) | <.001 | 0.94 (0.66 to 1.35) | .74 |
| Year2 | 0.98 (0.97 to 0.99) | .004 | 1.01 (0.99 to 1.03) | .29 |
| Age, y | ||||
| <40 | 0.50 (0.18 to 1.42) | .19 | 1.08 (0.27 to 4.43) | .91 |
| 40–49 | 0.55 (0.26 to 1.16) | .11 | 4.49 (1.65 to 2.23) | .003 |
| 50–64 | 0.63 (0.37 to 1.06) | .08 | 2.71 (1.44 to 5.12) | .002 |
| ≥65 | 1.00 (referent) | 1.00 (referent) | ||
| Race | ||||
| Black | 0.92 (0.41 to 2.06) | .84 | 2.24 (0.82 to 6.09) | .12 |
| Non-black | 1.00 (referent) | 1.00 (referent) | ||
| No. of comorbid conditions | ||||
| <2 | 1.00 (referent) | 1.00 (referent) | ||
| ≥2 | 0.79 (0.55 to 1.14) | .21 | 0.91 (0.58 to 1.45) | .71 |
| Histologic subtype | ||||
| Comedo | 0.77 (0.45 to 1.33) | .36 | 1.88 (0.91 to 3.92) | .09 |
| Cribriform | 1.56 (1.07 to 2.28) | .02 | 1.03 (0.65 to 1.65) | .90 |
| Multifocality | ||||
| Yes | 0.38 (0.22 to 0.67) | .001 | 2.33 (1.25 to 4.35) | .01 |
| Unknown | 0.46 (0.27 to 0.80) | .01 | 1.59 (0.91 to 2.79) | .10 |
| No | 1.00 (referent) | 1.00 (referent) | ||
| Extensive DCIS | ||||
| Yes | 0.27 (0.15 to 0.52) | <.001 | 0.74 (0.21 to 2.59) | .64 |
| No | 1.00 (referent) | 1.00 (referent) | ||
| Nuclear grade | ||||
| Low | 1.00 (referent) | 1.00 (referent) | ||
| Medium | 0.88 (0.45 to 1.72) | .72 | 2.73 (1.33 to 5.62) | .01 |
| High | 0.66 (0.32 to 1.35) | .25 | 6.18 (2.63 to 14.53) | <.001 |
| Unknown | 0.57 (0.30 to 1.07) | .08 | 3.59 (1.71 to 7.53) | .001 |
| Margins | ||||
| Negative (≥2 mm) | 1.00 (referent) | 1.00 (referent) | ||
| Close (<2 mm) | 0.74 (0.49 to 1.12) | .16 | 1.62 (0.98 to 2.70) | .06 |
| Positive | 0.07 (0.04 to 0.12) | <.001 | 0.46 (0.19 to 1.13) | .09 |
| Family history of breast cancer | ||||
| No | 1.00 (referent) | 1.00 (referent) | ||
| Yes | 0.48 (0.32 to 0.71) | <.001 | 0.63 (0.37 to 1.08) | .09 |
| Unknown | 1.03 (0.59 to 1.79) | .92 | 0.32 (0.16 to 0.63) | .001 |
| Method of detection | ||||
| Detected with mammogram | 1.85 (1.08 to 3.16) | .03 | 1.21 (0.60 to 2.46) | .60 |
| Palpable disease | 1.00 (referent) | 1.00 (referent) | ||
| Mammographic tumor size | ||||
| Unknown | 0.52 (0.26 to 1.05) | .07 | 0.47 (0.19 to 1.12) | .09 |
| Mammographic tumor size | 0.73 (0.55 to 0.97) | .03 | 0.80 (0.53 to 1.23) | .31 |
| Log pseudo-likelihood | 474.889 | −301.667 | ||
| Pseudo R2 | 0.283 | 0.273 | ||
| Test of physician fixed effects‡ | χ2 = 32.530 | .03 | χ2 = 51.340 | <.001 |
*
Multivariable logistic regression models: the breast-conserving surgery (BCS) model is a logistic regression of BCS vs mastectomy; the radiation therapy (RT) model is a logistic regression of RT vs no RT among women who had BCS. CI = confidence intervals; DCIS = ductal carcinoma in situ; OR = odds ratio.
†
Other covariates not shown include census level percent black, census level percent below poverty, insurance status and type, menopausal status, and calcifications.
‡
The test of the joint significance of the physician fixed effects: two-sided χ2 with 19 df.