Validation cohort from the University Medical Center Groningen
Study population:
This external validation group consisted of 439 patients who underwent BCT at the University Medical Center Groningen (UMCG), Groningen, The Netherlands between July 2004 and June 2008 or July 2009 and May 2011. A total of 331 patients (75%) were eligible for analysis.

Inclusion criteria: 
Women with clinical T1–2N0–1Mx–0 histology-proven invasive breast carcinoma who underwent BCT were included in the study.

Exclusion criteria: 
Patients with unconfirmed malignancy prior to surgery, undefined margin status, neo-adjuvant treatment, or absence of reported radiological tumor size were excluded. 
 
Research authors: Pleijhuis RG
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Discrimination

Rows included 331
C-index 0.69 | 95% CI: 0.621 - 0.7585 ROC
Brier score 0.175
Scaled Brier score 0.053

Classification plot

Calibration

Regression coefficient 1.221
Intercept 0.046
Hosmer-Lemeshow GOF 0.003
 

Calibration plot

Histogram

Decision curve

Comparison
Original study population: 1185
Validation study population: 331

Categorical characteristics

Name Subset / Group Nr. of patients Validation P-Value
Age <40 years 39 28 0.0005
40-70 years 919 255
>70 years 227 48
Tumor size pT1a 54 22 0.096
pT1b 243 81
pT1c 599 164
pT2 284 62
pT3 5 2
Area on mammogram <15.000 mm2 450 138 0.3558
15.000-25.000 mm2 554 142
>25.000 mm2 181 45
Weight excised <50 gram 270 167 0.1434
50-100 gram 172 78
>100 gram 165 82
Tumor-to-lump index <0.25 278 121 0.1209
0.25-0.50 228 135
>0.50 101 53
Palpability Palpable 637 195 0.1043
Non-palpable 548 136
Tumor location LOQ 122 42 0.0005
UOQ 535 170
UIQ 189 50
LIQ 150 26
Central 103 6
Histological type Ductal 957 286 0.061
Lobular 119 23
Specified 109 22
Histological grade Grade I 330 107 0.1999
Grade II 531 133
Grade III 313 86
ER status Positive 1002 276 0.661
Negative 172 51
PR status Positive 750 226 0.4434
Negative 300 101
Her2/neu receptor status Positive 125 40 0.4862
Negative 1041 290
Multifocal disease Yes 47 19 0.1707
No 1138 312
pN-stage Positive 310 113 0.0055
Negative 875 218
Prior surgery to the breast Yes 46 34 < 0.0001
No 1139 297
Family history FDR 91 75 0.0005
SDR 188 56
Negative 749 199
BI-RADS classification II 3 8 0.001
III 93 31
IV 611 155
V 447 127
Preoperative MRI Yes 122 31 0.6803
No 1063 300
Microcalcifications Yes 245 74 0.5421
No 937 257
DCIS component present Yes 529 188 0.0001
No 656 143
Breast density 0-25% 323 101 0.8061
25-50% 467 146
50-75% 217 70
75-100% 34 7
Institution University-affiliated 642 331 < 0.0001
Community hospital 543 0

Continuous characteristics

Name Mean SD Unit Plot
Original Validation Age 59.8
56.5
0.31
0.63
years
Original Validation Tumor size 15.6
15.2
0.22
0.48
mm
Original Validation Area on mammogram 17916
17575
6807
6937
mm2
Original Validation Weight excised lump 62.5
56.3
39.7
40.0
gram
Original Validation Tumor-to-lump index 0.338
0.354
0.012
0.020
(index)
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