Table 2. Comparison of ctDNA assay with CT scans to monitor resistance to anti-HER2 therapy.
| N (%) | CT | Concordance rate (%) a | Adjusted concordance rate (%) b | |
|---|---|---|---|---|
| Progression n=14 | Non-progression n=20 | |||
| HER2 amplification | 73.5 | 80.6 | ||
| Progression | 8 (57.1) | 3 (15.0) | ||
| Non-progression | 6 (42.9) | 17 (85.0) | ||
| Somatic mutations c | 58.8 | 69.0 | ||
| Progression | 8 (57.1) | 8 (40.0) | ||
| Non-progression | 6 (42.9) | 12 (60.0) | ||
| Combined ctDNA criteria | 67.6 | 82.1 | ||
| Progression | 12 (85.7) | 9 (45.0) | ||
| Non-progression | 2 (14.3) | 11 (55.0) | ||
a
Concordance rate=Number of consistent evaluations by ctDNA assay and CT/total number of evaluations×100%
b
In some cases, ctDNA assay detected drug resistance earlier than CT did, as confirmed by subsequent imaging assessment. In that situation, the discordant evaluations (progression by ctDNA/non-progression by CT) were ascribed to the inefficient reflection of tumor response by CT and consequently were excluded when calculating the concordance rate.
c
In this criterion, relevant mutations involve genes TP53/PIK3CA/MTOR/PTEN, all of which have been identified as potential markers of resistance to anti-HER2 therapy.