Patient characteristics. Between June 2010 and September 2016, there were 320 pT1-2N0-1M0 patients with HER2-positive breast cancer who underwent breast-conserving surgery or mastectomy in the training dataset. After excluding 6 cases of no ≥3 years of follow-up data, 18 cases with insufficient tumor proportion in H&E section and 42 cases with insufficient RNA/failure to pass quality control, 254 patients aged (49.3±9.6) years were finally eligible for the study to construct the prognostic model. As shown in Fig. 1, two independent clinical cohorts were used for external validation.
Among the patients enrolled in the training dataset, 52.8% were assessed for grade II, 52.8% for T2 and 62.6% for N0; 73.2% of patients had no LVI; 53.9% of patients showed ER-positive and PR-positive. All the patients received anti-HER2 therapy and adjuvant chemotherapy. Thirty-two patients experienced relapse, while 222 didn’t. The baseline characteristics of patients in training and two validation datasets are summarized in Table 1.
Table 1
Baseline characteristics of patients in training and validation datasets, n(%)
Characteristic
|
Training dataset (n=254)
|
External validation dataset
|
Validation cohort I (n=125)
|
Validation cohort II (n=24)
|
Age, years, mean (SD)
|
49.3 (9.6)
|
50.3 (9.5)
|
53.9 (12.6)
|
Histologic grade
|
|
|
|
Ⅰ
|
1 (0.4)
|
0 (0.0)
|
4 (16.7)
|
Ⅱ
|
134 (52.8)
|
58 (46.4)
|
15 (62.5)
|
Ⅲ
|
119 (46.9)
|
67 (53.6)
|
5 (20.8)
|
Tumor stage
|
|
|
|
T1
|
120 (47.2)
|
45 (36.0)
|
11 (45.8)
|
T2
|
134 (52.8)
|
80 (64.0)
|
9 (33.4)
|
T3
|
0 (0.0)
|
0 (0.0)
|
2 (8.3)
|
Unknown
|
0 (0.0)
|
0 (0.0)
|
2 (12.5)
|
Nodal stage
|
|
|
|
N0
|
159 (62.6)
|
89 (71.2)
|
8 (33.3)
|
N1
|
95 (37.4)
|
36 (28.8)
|
14 (58.3)
|
N2
|
0 (0.0)
|
0 (0.0)
|
2 (8.3)
|
LVI
|
|
|
|
Yes
|
68 (26.8)
|
36 (28.8)
|
12 (50.0)
|
No
|
186 (73.2)
|
89 (71.2)
|
10 (41.7)
|
Unknown
|
0 (0.0)
|
0 (0.0)
|
2 (8.3)
|
HR status
|
|
|
|
ER-/PR-
|
81 (31.9)
|
57 (45.6)
|
9 (37.5)
|
ER-/PR+
|
17 (6.7)
|
4 (3.2)
|
1 (4.2)
|
ER+/PR-
|
19 (7.5)
|
15 (12.0)
|
2 (8.3)
|
ER+/PR+
|
137 (53.9)
|
49 (39.2)
|
12 (50.0)
|
Anti-HER2 therapy
|
|
|
|
Yes
|
254 (100.0)
|
125 (100.0)
|
0 (0.0)
|
No
|
0 (0.0)
|
0 (0.0)
|
0 (0.0)
|
Unknown
|
-
|
-
|
24 (100.0)
|
Adjuvant chemotherapy
|
|
|
|
Yes
|
254 (100.0)
|
125 (100.0)
|
22 (91.7)
|
No
|
0 (0.0)
|
0 (0.0)
|
2 (8.3)
|
Relapse
|
|
|
|
Yes
|
32 (12.6)
|
12 (9.6)
|
6 (25.0)
|
No
|
222 (87.4)
|
113 (90.4)
|
18 (75.0)
|
Notes: LVI, lymphovascular invasion; HR, hormone receptor; ER, estrogen receptor; PR, progesterone receptor; HER2, human epidermal growth factor receptor 2.
Performance and validation of HER2RI and HER2RIclin models. In the training cohort, the accuracy (proportion of correct predictions) of the HER2RI model for predicting the risk of recurrence and survival was 100%, with the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of 100% for each. The HER2RIclin model also achieved an unexceptionable accuracy of 100%, with sensitivity, specificity, PPV, and NPV of 100% for each (Table 2; Supplementary Figure 1). These results indicated the same excellent predictive performance of HER2RI and HER2RIclin models in the training cohort, which may be attributed to use of the RF based on machine learning method.
Two cohorts involving 125 and 24 HER2-poisitve patients were respectively used for external validation of both HER2RI and HER2RIclin models. The predictive accuracy of the HER2RI model was 90.4% in validation cohort I and 83.3% in validation cohort II, while that of the HER2RIclin model was 84.0% in validation cohort I and 81.8% in validation cohort II (Table 2; Supplementary Figure 1). Overall, the HER2RI model presented a superior predictive accuracy in both validation cohorts.
Table 2
Predictive performance of the HER2RI and HER2RIclin models in the training and validation datasets
Datasets
|
HER2RI model
|
HER2RIclin model
|
Relapse
|
Yes (%)
|
No (%)
|
p-value
|
Relapse
|
Yes (%)
|
No (%)
|
p-value
|
Training dataset (n=254)
|
Risk category
|
|
|
<0.001
|
Risk category
|
|
|
<0.001
|
High
|
32 (100.0)
|
0 (0.0)
|
|
High
|
32 (100.0)
|
0 (0.0)
|
|
Low
|
0 (0.0)
|
222 (100.0)
|
Low
|
0 (0.0)
|
222 (100.0)
|
Total
|
32
|
222
|
Total
|
32
|
222
|
Accuracy=1.000; Sensitivity=1.000; Specificity=1.000; PPV=1.000; NPV=1.000
|
Accuracy=1.000; Sensitivity=1.000; Specificity=1.000; PPV=1.000; NPV=1.000
|
Validation dataset I (n=125)
|
Risk category
|
|
|
0.003
|
Risk category
|
|
|
0.323
|
High
|
4 (50.0)
|
4 (50.0)
|
|
High
|
2 (16.7)
|
10 (83.3)
|
|
Low
|
8 (6.8)
|
109 (93.2)
|
Low
|
10 (8.8)
|
103 (91.2)
|
Total
|
12
|
113
|
Total
|
12
|
113
|
Accuracy=0.904; Sensitivity=0.333; Specificity=0.965; PPV=0.500; NPV=0.932
|
Accuracy=0.840; Sensitivity=0.167; Specificity=0.912; PPV=0.167; NPV=0.912
|
Validation dataset II* (n=24)
|
Risk category
|
|
|
0.054
|
Risk category
|
|
|
0.046
|
High
|
2 (100.0)
|
0 (0.0)
|
|
High
|
3 (75.0)
|
1 (25.0)
|
|
Low
|
4 (18.2)
|
18 (81.8)
|
Low
|
3 (16.7)
|
15 (83.3)
|
Total
|
6
|
18
|
Total
|
6
|
16
|
Accuracy=0.833; Sensitivity=0.333; Specificity=1.000; PPV=1.000; NPV=0.818
|
Accuracy=0.818; Sensitivity=0.500; Specificity=0.938; PPV=0.750; NPV=0.833
|
Notes: “*” represents 2 cases are excluded from the HER2RIclin model due to lack of nodal stage.
PPV, Positive predictive value; NPV, negative predictive value.
Survival outcomes based on HER2RI and HER2RIclin models. In the training cohort, there were 222 patients assessed as low risk and 32 as high risk based on the cut-off 0.36 of the risk score in the HER2RI model or the cut-off 0.32 of the risk score in the HER2RIclin model. The difference was pronounced between low- and high-risk patients regarding nodal stage (p=0.018) (Table 3). In validation cohort I, 117 cases were assessed as low risk and 8 as high risk by the HER2RI model, while 113 cases were classified as low risk and 12 as high risk using the HER2RIclin model. In validation cohort II, there were 22 cases at low risk and 2 at high risk through the HER2RI model, 18 cases at low risk and 4 at high risk using the HER2RIclin model. The clinicopathological characteristics of low- and high-risk patients stratified by the HER2RI and HER2RIclin models in both validation datasets are compared in Supplementary Table 2-3.
Table 3
Clinicopathological characteristics of low- and high-risk patients stratified by the HER2RI/HER2RIclin model, n(%)
Characteristics
|
HER2RI/HER2RIclin model (n=254)
|
Low-risk (n=222)
|
High-risk (n=32)
|
p-value
|
Age, years, mean (SD)
|
49.6 (9.5)
|
47.6 (10.7)
|
0.274
|
Histologic grade
|
|
|
0.746
|
Ⅰ
|
1 (0.5)
|
0 (0.0)
|
|
Ⅱ
|
116 (52.3)
|
18 (56.3)
|
|
Ⅲ
|
105 (47.3)
|
14 (43.7)
|
|
Tumor stage
|
|
|
0.275
|
T1
|
102 (45.9)
|
18 (56.3)
|
|
T2
|
120 (54.1)
|
14 (43.7)
|
|
Nodal stage
|
|
|
0.018
|
N0
|
145 (65.3)
|
14 (43.7)
|
|
N1
|
77 (34.7)
|
18 (56.3)
|
|
LVI
|
|
|
0.853
|
Yes
|
59 (26.6)
|
9 (28.1)
|
|
No
|
163 (73.4)
|
23 (71.9)
|
|
HR status
|
|
|
0.534
|
ER-/PR-
|
69 (31.1)
|
12 (37.5)
|
|
ER-/PR+
|
14 (6.3)
|
3 (9.4)
|
|
ER+/PR-
|
16 (7.2)
|
3 (9.4)
|
|
ER+/PR+
|
123 (55.4)
|
14 (43.8)
|
|
Notes: LVI, lymphovascular invasion; HR, hormone receptor; ER, estrogen receptor; PR, progesterone receptor; HER2, human epidermal growth factor receptor 2.
Fig. 2 depicts the 7-year RFS rates of patients at low and high risk assessed by the HER2RI model. It could be observed that the low-risk patients in the training dataset showed a better 7-year RFS rate than the high-risk patients (p<0.0001; Fig. 2a). As expected, statistically significant differences in 5-year RFS rates were shown between the low- and high-risk patients whether in validation cohort I (p<0.0001; Fig. 2b) or in validation cohort II (p<0.0001; Fig. 2c). Regarding the 7-year RFS rates of high- and low-risk patients stratified by the HER2RIclin model, the significant difference was shown in the training cohort (p<0.0001; Fig. 3a). Despite no statistically significant differences in validation cohort I, there existed a tendency of a higher 5-year RFS rate in low-risk patients than high-risk patients (p=0.183; Fig. 2b). Additionally, in the validation cohort II, the 5-year RFS rate of patients at low risk classified by the HER2RIclin model was also significantly higher than those at high risk (p=0.00083; Fig. 3c).
Association of the model predictors with prognosis. Uni- and multivariate analyses of the validation cohort I were performed to examine whether the predictors derived from the HER2RI and HER2RIclin models could be an independent factor for RFS (Table 4). It could be observed that RFS was not under the influence of the clinicopathological factors, such as age, histologic grade, tumor stage, nodal stage, LVI and HR status, while the HER2RI model was a significant determinant for RFS. Compared with low-risk patients, high-risk patients stratified by the HER2RI had a significantly shortened RFS (HR: 12.972, 95%CI: 3.124-53.868, p<0.001).
Table 4
Cox proportional hazards regression analysis for recurrence-free survival of patients included in validation cohort I
Variables
|
Univariate
|
Multivariate (HER2RI)
|
Multivariate (HER2RIclin)
|
HR (95% CI)
|
p-value
|
HR (95% CI)
|
p-value
|
HR (95% CI)
|
p-value
|
Age, years
|
|
|
|
|
|
|
≤40
|
Reference
|
|
Reference
|
|
Reference
|
|
>40
|
0.636 (0.134-3.018)
|
0.569
|
1.379 (0.166-11.449)
|
0.766
|
0.759 (0.143-4.020)
|
0.746
|
Histologic grade
|
|
|
|
|
|
|
Ⅱ
|
Reference
|
|
Reference
|
|
Reference
|
|
Ⅲ
|
3.929 (0.848-18.214)
|
0.080
|
2.783 (0.512-15.122)
|
0.236
|
2.657 (0.529-13.343)
|
0.235
|
Tumor stage
|
|
|
|
|
|
|
T1
|
Reference
|
|
Reference
|
|
Reference
|
|
T2
|
1.763 (0.464-6.697)
|
0.405
|
1.930 (0.299-12.465)
|
0.490
|
1.710 (0.300-9.730)
|
0.546
|
Nodal stage
|
|
|
|
|
|
|
N0
|
Reference
|
|
Reference
|
|
Reference
|
|
N1
|
2.706 (0.783-9.353)
|
0.116
|
1.543 (0.292-8.143)
|
0.610
|
1.111 (0.218-5.652)
|
0.899
|
LVI
|
|
|
|
|
|
|
No
|
Reference
|
|
Reference
|
|
Reference
|
|
Yes
|
3.810 (1.072-13.540)
|
0.039
|
3.536 (0.767-16.306)
|
0.105
|
3.394 (0.731-15.747)
|
0.119
|
HR status
|
|
|
|
|
|
|
HR-
|
Reference
|
|
Reference
|
|
Reference
|
|
HR+
|
0.301 (0.080-1.135)
|
0.076
|
0.334 (0.071-1.575)
|
0.166
|
0.260 (0.064-1.064)
|
0.061
|
HER2RI model
|
|
|
|
|
|
|
Low risk
|
Reference
|
|
Reference
|
|
|
|
High risk
|
13.644 (3.816-48.789)
|
<0.001
|
12.972 (3.124-53.868)
|
<0.001
|
|
|
HER2RIclin model
|
|
|
|
|
|
|
Low risk
|
Reference
|
|
|
|
Reference
|
|
High risk
|
2.375 (0.504-11.193)
|
0.274
|
|
|
0.730 (0.141-3.782)
|
0.708
|
Notes: LVI, lymphovascular invasion; HR, hormone receptor; HR (95%CI), hazard ratio (95% confidence interval).