Patient characteristics and ctDNA detection. Out of the 12 patients included in this study, eight (83.3%) were male and nine (75.0%) had smoking history (Fig. 1). While eight (83.3%) patients had adenocarcinoma, eight (83.3%) were diagnosed with stage IV NSCLC. Pneumonia was observed in two patients (P8 and P12) during follow-ups (Table 1). Necrosis of primary tumor was observed in two patients (P3 and P8). TB gradually increased in 11 (91.7%) patients except P8. In P8, the size of the solid tumor temporarily decreased slightly in proportion to the increase in necrotic area. The median duration of follow-ups was 298 days. Death was observed in 11 patients. The median survival of the patients was 235 days.
Table 1
Patient characteristics and circulating tumor DNA detection
Patient | Timea | ctDNA detection | VDT (days) | Pneumonia | Tumor necrosis |
P1 | T1 | Yes | 130 | | |
T2 | | |
T3 | | |
T4 | | |
P2 | T1 | No | 221 | | |
T2 | | |
T3 | | |
P3 | T1 | Yes | 73 | | Yes |
T2 | | Yes |
P4 | T1 | No | 60 | | |
T2 | | |
P5 | T1 | No | 179 | | |
T2 | | |
T3 | | |
P6 | T1 | Yes | 48 | | |
T2 | | |
T3 | | |
P7 | T1 | No | 213 | | |
T2 | | |
T3 | | |
P8 | T1 | No | 150 | Yes | Yes |
T2 | | Yes |
T3 | Yes | Yes |
P9 | T1 | Yes | 130 | | |
T2 | | |
T3 | | |
P10 | T1 | Yes | 53 | | |
T2 | | |
P11 | T1 | Yes | 44 | | |
T2 | | |
P12 | T1 | Yes | 142 | Yes | |
T2 | | |
T3 | Yes | |
aT1 to T4 denote a time point for plasma sampling and imaging tests.
ctDNA, circulating tumor DNA; VDT, volume doubling time
CtDNA was detected in the plasma of 7 (58.3%) patients (Supplementary Table S1 online). The median ctDNA level was 9.1 hGE/ml (range: 0.8–108.5) and the median variant allele frequency was 4.2% (range 0.1–21.9). Patients with detected ctDNA showed a trend to be male, have smoking history, have adenocarcinoma, and/or be diagnosed at advanced stages. The most common mutations detected were in TP53 (five patients [41.7%]), followed by those in CSMD3, FAT1, ARID1B, TULP4, DST, PCDH15, PKHD1L1, and LRP1B. The results of validation ddPCR were comparable to those of NGS in the patients with detected ctDNA (Supplementary Table S2 online).
Change in ctDNA levels and tumor burden. Four patients (57.1%) with detected ctDNA (P6, P9, P10, and P11) displayed a tendency of increasing ctDNA levels over time, which may correspond to increase in TB (Fig. 2). By contrast, changes of ctDNA levels in the other three patients (P1, P3, and P12) showed discordance with increase in TB. Several distinct clinical features were accompanied in these patients. In P1, although the primary tumor size gradually decreased, the total TB gradually increased as the size of the brain metastasis increased. In P3, the size of the primary tumor slightly increased whereas the area with accompanied tumor necrosis decreased. Pneumonia was occurred at the diagnosis and the third follow-up period in P12.
Volume doubling time and overall survival regarding ctDNA detection at diagnosis. The median value of VDT in the patients whose ctDNA was detected at diagnosis was 73 days. The patients whose ctDNA was not detected displayed a longer median VDT, 179 days (p = 0.039) (Fig. 3). Of note, the patients with detected ctDNA had a significantly worse OS than those without detected ctDNA (the median OS of 153 days versus 501 days, log-rank p = 0.019) (Fig. 4). Moreover, patients with high-level ctDNA had worse OS compared with those with low-level ctDNA (the median OS of 121 days versus 235 days, log-rank p = 0.048).