Table 1. Descriptive characteristics of the study population.
| Characteristics | Overall (N = 8015) |
|---|---|
| Year of diagnosis % (N) | |
| 2001–2002 | 25.6 (2072) |
| 2003–2004 | 24.4 (1952) |
| 2005–2006 | 25.8 (2064) |
| 2007–2008 | 24.0 (1927) |
| Age at diagnosis % (N) | |
| <50 years | 23.0 (1842) |
| 50–65 years | 51.3 (4111) |
| >65 years | 25.7 (2062) |
| Menopausal status % (N) | |
| Premenopausal | 30.4 (2289) |
| Postmenopausal | 69.6 (5251) |
| Missing (N) | 475 |
| Stage % (N) | |
| Stage I | 48.2 (3690) |
| Stage II | 39.4 (3014) |
| Stage III | 12.4 (948) |
| Missing (N) | 363 |
| Tumor size % (N) | |
| ≤2 cm | 25.7 (2000) |
| 2–5 cm | 44.0 (3418) |
| > 5 cm | 30.3 (2351) |
| Missing (N) | 246 |
| Comorbidity % (N) | |
| None | 90.1 (7222) |
| 1 | 5.5 (439) |
| ≥2 | 4.4 (354) |
| History of hypertension | |
| No | 94.6 (7579) |
| Yes | 5.4 (436) |
| History of chronic pulmonary disease or tobacco abuse | |
| No | 96.6 (7746) |
| Yes | 3.4 (269) |
| Surgery % (N) | |
| No | 1.0 (79) |
| Yes, breast-conserving | 60.7 (4852) |
| Yes, mastectomy | 38.3 (3058) |
| Missing (N) | 26 |
| Radiotherapy % (N) | |
| No | 22.5 (1774) |
| Yes, left-sided | 37.5 (2962) |
| Yes, right-sided | 39.1 (3088) |
| Yes, both-sided | 0.85 (67) |
| Missing (N) | 124 |
| Chemotherapy % (N) | |
| No | 58.5 (4604) |
| Yes | 41.5 (3262) |
| Missing (N) | 149 |
| Hormone therapy % (N) | |
| No | 18.10 (1424) |
| Yes, tamoxifen | 53.0 (4247) |
| Yes, aromatase inhibitors | 19.3 (1550) |
| Yes, type unknown | 8.1 (645) |
| Missing (N) | 149 |
| Trastuzumab therapy % (N) * | |
| No | 87.3 (2180) |
| Yes | 12.7 (316) |
| Missing (N) | 1497 |
*
Missingness on individual variables is less than 5%, except for menopausal status (5.9%, N = 488). Treatment-specific analysis of trastuzumab was restricted to patients diagnosed between 2005 and 2008 (missingness = 37.5%, N = 1497).