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Table 1 Average genotyping score, assigned score criteria and error rates for every case analysed by the pilot scheme participants

From: International pilot external quality assessment scheme for analysis and reporting of circulating tumour DNA

Sample

A

B

C

D

E

F

G

H

I

J

A-J

Variant status

5% KRAS c.35G>C; p.(G12A)

1% KRAS c.35G>C; p.(G12A)

5% NRAS c.182A>G; p.(Q61R)

1% NRAS c.182A>G; p.(Q61R)

KRAS/NRAS Wild-type

5% EGFR c.2235_2249del15; p.E746_A750del

1% EGFR c.2235_2249del15; p.E746_A750del

5% EGFR c.2573T>G; p.(L858R) and c.2369C>T; p.(T790M)

1% EGFR c.2573T>G; p.(L858R) and c.2369C>T; p.(T790M)

EGFR Wild-type

Overall

Average score per sample on 2 points

1.5

1.3

1.7

1.5

2.0

1.7

1.7

1.9

1.6

1.9

1.7

Score criteria

# obtained scores (%)

 Correct (2 points)

11 (35.5%)

7 (22.6%)

12 (38.7%)

8 (25.8%)

23 (74.2%)

5 (16.1%)

4 (12.9%)

29 (93.5%)

18 (58.1%)

30 (96.8%)

147 (47.4%)

 Correct but unspecified (2 points)

5 (16.1%)

3 (9.7%)

4 (12.9%)

2 (6.5%)

0 (0.0%)

16 (51.6%)

16 (51.6%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

46 (14.8%)

 False-negative ≤ LOD (2 points)a

0 (0.0%)

5 (16.1%)

0 (0.0%)

4 (12.9%)

0 (0.0%)

0 (0.0%)

2 (6.5%)

0 (0.0%)

6 (19.4%)

0 (0.0%)

17 (5.5%)

 False-negative but variant not tested for (2 points)a

0 (0.0%)

0 (0.0%)

3 (9.7%)

3 (9.7%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

6 (1.9%)

 False-negative >/unknown LOD (0 points)a

1 (3.2%)

5 (16.1%)

3 (9.7%)

4 (12.9%)

0 (0.0%)

0 (0.0%)

1 (3.2%)

0 (0.0%)

3 (9.7%)

0 (0.0%)

17 (5.5%)

 False-positive (0 points)a

2 (6.5%)

2 (6.5%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

1 (3.2%)

0 (0.0%)

0 (0.0%)

1 (3.2%)

6 (1.9%)

 Incorrect mutation detected with therapeutic implications (0 points)a

0 (0.0%)

0 (0.0%)

1 (3.2%)

1 (3.2%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

2 (0.6%)

 Incorrect mutation detected without therapeutic implications (2 points)

3 (9.7%)

1 (3.2%)

0 (0.0%)

1 (3.2%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

5 (1.6%)

 One variant missed in double mutation sample (0 points)a

N/A

N/A

N/A

N/A

N/A

N/A

N/A

2 (6.5%)

4 (12.9%)

N/A

6 (1.9%)

 Mutation described incorrectly (1 point)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

10 (32.3%)

6 (19.4%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

16 (5.2%)

 Technical failure (not scored)

1 (3.2%)

0 (0.0%)

0 (0.0%)°

0 (0.0%)°

0 (0.0%)

0 (0.0%)

1 (3.2%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

2 (0.6%)

 Not tested (not scored)

8 (25.8%)

8 (25.8%)

8 (25.8%)

8 (25.8%)

8 (25.8%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

0 (0.0%)

40 (12.9%)

 Total scored (n = 31)

22 (71.0%)

23 (74.2%)

23 (74.2%)

23 (74.2%)

23 (74.2%)

31 (100.0%)

30 (96.8%)

31 (100.0%)

31 (100.0%)

31 (100.0%)

268 (86.5%)

Error rate

# obtained scores (%)

 Total with implication on therapy decisiona

3 (13.6%)

12 (52.2%)

7 (30.4%)

12 (52.2%)

0 (0.0%)

0 (0.0%)

4 (13.3%)

2 (6.5%)

13 (41.9%)

1 (3.2%)

54 (20.1%)

Gene not tested/No method info given

0

0

3

3

0

0

0

0

0

0

6

NGS

2

7

3

7

0

0

1

1

7

1

29

Commercial Kit

0

3

1

1

0

0

0

0

1

0

6

LDT

1

1

0

0

0

0

1

0

1

0

4

BEAMing

0

0

0

0

0

0

0

0

0

0

0

ddPCR

0

1

0

1

0

0

2

1

4

0

9

  1. N/A Not applicable
  2. aValues were used to calculate the error rates. °One partial technical failure for NRAS, only correct KRAS WT status was assessed on these cases. Reference sequence at time of scoring: EGFR: NM_005228.4 or LRG_304t1; KRAS: NM_033360.3 or NM_004985.4; NRAS: NM_002524.4 or LRG_92t1. Methods are ranked from least to more sensitive techniques as reported in literature: NGS 1–3%, commercial kit 0.1%, BEAMing 0.01%, ddPCR 0.001% [28]. For the LDT, a LOD of 0.1% was reported by the laboratory. Abbreviations: BEAMing Beads, emulsification, amplification, and magnetics, ddPCR Droplet digital polymerase chain reaction, LDT Laboratory-developed test, NGS Next-generation sequencing