Correlation of circulating tumour DNA shedding in patient plasma with demographics and clinical features of patients treated at University Health Network
| Characteristic | All patients (n=107) | Shedders* of circulating tumour DNA (n=48) | Non-shedders of circulating tumour DNA (n=59) | P value |
| Age, N | 103 | 46 | 57 | 0.66 |
| Mean, years (SD) | 65.6 (12.9) | 65.2 (12.6) | 66 (13.3) | |
| Median, years (min, max) | 64 (31, 99) | 63 (39, 88) | 65 (31, 99) | |
| Sex, N | 106 | 47 | 59 | 0.69 |
| Male, N (%) | 66 (62) | 28 (60) | 38 (64) | |
| Female, N (%) | 40 (38) | 19 (40) | 21 (36) | |
| Smoking status, N | 104 | 47 | 57 | 1 |
| Never, N (%) | 27 (26) | 12 (26) | 15 (26) | |
| Former, N (%) | 77 (74) | 35 (74) | 42 (74) | |
| Number of metastatic sites, N | 105 | 46 | 59 | 0.0012 |
| Mean, N (SD) | 3.4 (1.6) | 3.9 (1.3) | 2.9 (1.7) | |
| Median, N (min, max) | 3 (0, 9) | 4 (2, 7) | 3 (0, 9) | |
| Metastases, N | 104 | 46 | 58 | |
| CNS, N (%) | 51 (49) | 22 (48) | 29 (50) | 0.85 |
| Bone, N (%) | 56 (54) | 31 (67) | 25 (43) | 0.018 |
| Liver, N (%) | 18 (17) | 13 (28) | 5 (9) | 0.017 |
| Lymph node, N (%) | 61 (59) | 30 (65) | 31 (53) | 0.24 |
| Adrenal, N (%) | 12 (12) | 6 (13) | 6 (11) | 0.76 |
| None (disease in lung only), N (%) | 9 (9) | 0 (0) | 9 (16) | 0.004 |
| Size of large tumour, N | 79 | 40 | 39 | 0.31 |
| Mean, mm (SD) | 3 (2.7) | 3.3 (3.2) | 2.7 (2.1) | |
| Median, mm (range) | 2.2 (0.3, 19) | 2.5 (0.3, 19) | 2.1 (0.4, 10.8) | |
| Prior TKI treatment, N | 104 | 46 | 58 | 0.67 |
| First-generation (gefitinib, erlotinib), N (%) | 95 (91) | 42 (91) | 53 (91) | |
| Second-generation (afatinib), N (%) | 9 (9) | 4 (9) | 5 (9) | |
| TKI treatment duration, N | 103 | 47 | 56 | 0.96 |
| Mean, days (SD) | 523.2 (419.1) | 502.2 (367.6) | 540.9 (460.4) | |
| Median, days (min, max) | 419 (28, 2149) | 423 (28, 2015) | 406 (30, 2149) | |
| LDH levels, N | 93 | 43 | 50 | 0.54 |
| ≤220 U/L, N (%) | 47 (51) | 20 (47) | 27 (54) | |
| >220 U/L, N (%) | 46 (49) | 23 (53) | 23 (46) | |
| EGFR sensitising mutation, N | 83 | 43 | 40 | 0.11 |
| L858R, N (%) | 35 (42) | 18 (42) | 17 (42) | |
| Exon 19 deletion, N (%) | 44 (53) | 25 (58) | 19 (48) | |
| Other (G719S/C/A, L861Q, N771delinsHV), N (%) | 4 (5) | 0 (0) | 4 (10) |
*Shedders of tumour DNA are defined as patients with a positive plasma test result for either the epidermal growth factor receptor (EGFR) sensitising mutation (L858R or exon 19 deletion) or resistance mutation (T790M), as a measure of the presence of tumour DNA within the plasma specimen.
CNS, central nervous system; LDH, lactate dehydrogenase; TKI, tyrosine kinase inhibitor.