Table 1.
Comparison of baseline characteristics of patients who underwent breast‐conserving surgery according to time to chemotherapy ≤30 days and >30 days before and after matching
| Before matching (n = 1,079) | After matching (n = 904) | |||||
|---|---|---|---|---|---|---|
| ≤30 days (n = 485) | >30 days (n = 594) | Standardized difference | ≤30 days (n = 452) | >30 days (n = 452) | Standardized difference | |
| Year of inclusion | ||||||
| 2006 | 32 (6.6) | 51 (8.6) | 0.075 | 31 (6.9) | 27 (6.0) | 0.036 |
| 2007 | 31 (6.4) | 42 (7.1) | 0.027 | 31 (6.9) | 36 (8.0) | 0.042 |
| 2008 | 55 (11.3) | 69 (11.6) | 0.009 | 54 (11.9) | 59 (13.1) | 0.033 |
| 2009 | 51 (10.5) | 71 (12.0) | 0.046 | 51 (11.3) | 54 (11.9) | 0.021 |
| 2010 | 57 (11.8) | 106 (17.9) | 0.172 | 57 (12.6) | 37 (8.2) | 0.145 |
| 2011 | 68 (14.0) | 74 (12.5) | 0.046 | 67 (14.8) | 71 (15.7) | 0.025 |
| 2012 | 70 (14.4) | 69 (11.6) | 0.084 | 63 (13.9) | 67 (14.8) | 0.025 |
| 2013 | 48 (9.9) | 64 (10.8) | 0.029 | 48 (10.6) | 54 (11.9) | 0.042 |
| 2014 | 73 (15.1) | 48 (8.1) | 0.219 | 50 (11.1) | 47 (10.4) | 0.021 |
| Age (years) | ||||||
| <40 | 79 (16.3) | 93 (15.7) | 0.017 | 77 (17.0) | 78 (17.3) | 0.006 |
| 40–49 | 157 (32.4) | 147 (24.8) | 0.169 | 138 (30.5) | 141 (31.2) | 0.014 |
| 50–59 | 134 (27.6) | 198 (33.3) | 0.124 | 131 (29.0) | 125 (27.7) | 0.029 |
| 60–69 | 101 (20.8) | 140 (23.6) | 0.066 | 93 (20.6) | 94 (20.8) | 0.005 |
| ≥70 | 14 (2.9) | 16 (2.7) | 0.012 | 13 (2.9) | 14 (3.1) | 0.013 |
| SES | ||||||
| Low | 149 (30.7) | 183 (30.8) | 0.002 | 139 (30.8) | 134 (29.6) | 0.024 |
| Medium | 167 (34.4) | 199 (33.5) | 0.020 | 156 (34.5) | 157 (34.7) | 0.005 |
| High | 169 (34.9) | 212 (35.7) | 0.018 | 157 (34.7) | 161 (35.6) | 0.029 |
| Histological tumor type | ||||||
| Ductal | 436 (89.9) | 544 (91.6) | 0.058 | 410 (90.7) | 407 (90.0) | 0.023 |
| Lobular | 6 (1.2) | 6 (0.8) | 0.039 | 3 (0.7) | 4 (0.9) | 0.025 |
| Other | 43 (8.9) | 45 (7.6) | 0.047 | 39 (8.6) | 41 (9.1) | 0.016 |
| Differentiation grade | ||||||
| Well | 3 (0.6) | 6 (1.0) | 0.044 | 3 (0.7) | 2 (0.4) | 0.030 |
| Intermediate | 58 (12.0) | 65 (10.9) | 0.032 | 48 (10.6) | 53 (11.7) | 0.035 |
| Poor | 419 (86.4) | 505 (85.0) | 0.039 | 396 (87.6) | 395 (87.4) | 0.007 |
| Unknown | 5 (1.0) | 18 (3.0) | 0.142 | 5 (1.1) | 2 (0.4) | 0.076 |
| Stage | ||||||
| I | 136 (28.0) | 193 (32.5) | 0.096 | 134 (29.6) | 124 (27.4) | 0.049 |
| II | 286 (59.0) | 312 (52.5) | 0.130 | 259 (57.3) | 266 (58.8) | 0.031 |
| III | 63 (13.0) | 89 (15.0) | 0.058 | 59 (13.1) | 62 (13.7) | 0.019 |
| Re‐excision | ||||||
| Yes | 33 (6.8) | 27 (4.6) | 0.098 | 22 (4.9) | 24 (5.3) | 0.020 |
| Change in hospital | ||||||
| Yes | 154 (31.8) | 217 (36.5) | 0.101 | 146 (32.3) | 136 (30.1) | 0.048 |
Note: Values are numbers (percentages) unless stated otherwise. Percentages may not add up to exactly 100% as a result of rounding.
A standardized difference of a variable of ≥10% is presented in bold. This indicates an imbalance in baseline characteristics between the time interval groups.
Abbreviations: SD, standard deviation; SES, socioeconomic status.