Table 1 Prevalence of key biomarkers at baseline

HER2, n (%)

221 (100.0)

223 (100.0)

 ISH+/IHC3+

184 (83.3)

185 (83.0)

 ISH+/IHC2+

25 (11.3)

26 (11.7)

 ISH+/IHC0 or 1+

2 (0.9)

0 (0)

 ISH−/IHC3+

1 (0.5)

2 (0.9)

 ISH−/IHC2+

0 (0)

1 (0.4)^a

 ISH unknown/IHC3+

9 (4.1)

8 (3.6)

 ISH unknown/IHC2+

0 (0)

1 (0.4)^a

HER2/CEP17 gene ratio, n (%)

211 (95.5)

210 (94.2)

 ≥ 2 to < 4

45 (21.3)

52 (24.8)

 ≥ 4

166 (78.7)

158 (75.2)

HER2 staining fraction, n (%)

221 (100.0)

223 (100.0)

 Focal (< 30%)

15 (6.8)^b

16 (7.2)

 Heterogeneous (30–79%)

27 (12.2)

27 (12.1)

 Homogeneous (≥ 80%)

179 (81.0)

180 (80.7)

HER2 mRNA expression^c

213 (96.4)

217 (97.3)

 Median (range)

36.3 (1.7–1606.8)

35.3 (2.0–548.8)

 ≤ median, n (%)

106 (49.8)

109 (50.2)

 > median, n (%)

107 (50.2)

108 (49.8)

HER3 mRNA expression^c

212 (95.9)

218 (97.8)

 Median (range)

0.3 (0–2.0)

0.3 (0–2.4)

 ≤ median, n (%)

101 (47.6)

116 (53.2)

 > median, n (%)

111 (52.4)

102 (46.8)

PIK3CA mutation status, n (%)

213 (96.4)

212 (95.1)

 Mutated

53 (24.9)

61 (28.8)

 Non-mutated

160 (75.1)

151 (71.2)

PAM50 subtype, n (%)

171 (77.4)

183 (82.1)

 HER2-E

104 (60.8)

90 (49.2)

 Luminal A

25 (14.6)

35 (19.1)

 Luminal B

32 (18.7)

42 (23.0)

 Basal-like

10 (5.8)

16 (8.7)

PD-L1, n (%)

200 (90.5)

196 (87.9)

 IC 0

117 (58.5)

106 (54.1)

 IC 1, 2, 3

83 (41.5)

90 (45.9)