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Table 2 Concordance of HER2 status by RT-PCR, IHC, and FISH

From: The relationship between quantitative human epidermal growth factor receptor 2 gene expression by the 21-gene reverse transcriptase polymerase chain reaction assay and adjuvant trastuzumab benefit in Alliance N9831

  

HER2 status by RT-PCR

Concordancea

Positive concordance and negative concordance

  

Negative

Equivocal

Positive

Total

n (%)

n (%)

n (%)

n (%)

 

Central HER2 IHC

0

14 (1.6)

1 (0.1)

1 (0.1)

16 (1.8)

87.6 %

Pos. concordance = 87.8 %

1+

19 (2.1)

6 (0.7)

0 (0.0)

25 (2.8)

Neg. concordance = 86.6 %

2+

58 (6.5)

25 (2.8)

18 (2.0)

101 (11.2)

(Ref = IHC)

3+

39 (4.3)

53 (5.9)

664 (73.9)

756 (84.2)

 

Total

130 (14.5)

85 (9.5)

683 (76.1)

898

  

HER2 status by RT-PCR

 

84.4 %

Pos. concordance = 83.8 %

  

Negative

Equivocal

Positive

Total

n (%)

n (%)

n (%)

n (%)

Neg. concordance = 89.8 %

Central HER2 FISH ratio

<2

62 (7.0)

17 (1.9)

9 (1.0)

88 (10.0)

(Ref = FISH)

≥2

64 (7.2)

65 (7.4)

667 (75.5)

796 (90.0)

 

Total

126 (14.3)

82 (9.3)

676 (76.5)

884

  

Central HER2 FISH ratio

 

85.8 %

Pos. concordance = 88.9 % (Ref = FISH)

  

<2

≥2

Total

n (%)

n (%)

n (%)

Central HER2 IHC

0

14 (1.6)

2 (0.2)

16 (1.8)

1+

14 (1.6)

10 (1.1)

24 (2.7)

Neg. concordance = 58.0 % (Ref = FISH)

2+

23 (2.6)

76 (8.6)

99 (11.2)

3+

37 (4.2)

706 (80.0)

743 (84.2)

 

Total

88 (10.0)

794 (90.0)

882

  1. Positive concordance = (number of results positive by both methods)/(number of results positive by reference method)
  2. Negative concordance = (number of results negative by both methods)/(number of results negative by reference method)
  3. HER2 human epidermal growth factor receptor 2, RT-PCR reverse transcriptase polymerase chain reaction, IHC immunohistochemistry, FISH fluorescence in situ hybridization
  4. aPer 2013 ASCO/CAP guidelines, equivocal values are classified as HER2 negative for purposes of calculating concordance. Hence, IHC = 0, 1+ and 2+ are classified as HER2 negative and HER2 equivocal by RT-PCR is classified as HER2 negative