Circulating tumour cells (CTCs) can be used to monitor cancer longitudinally, but their use in non-small cell lung cancer (NSCLC) is limited due to low numbers in the peripheral blood. Through diagnostic leukapheresis (DLA) CTCs can be obtained from larger blood volumes.

Patients with all stages of NSCLC were selected. One total body blood volume was screened by DLA before and after treatment. Peripheral blood was drawn pre- and post DLA for CTC enumeration by CellSearch. CTCs were detected in the DLA product (volume equalling 2 × 10⁸ leucocytes) and after leucocyte depletion (RosetteSep, 9 mL DLA product). Single-cell, whole-genome sequencing was performed on isolated CTCs.

Fifty-six patients were included. Before treatment, CTCs were more often detected in DLA (32/55, 58%) than in the peripheral blood (pre-DLA: 18/55, 33%; post DLA: 13/55, 23%, both at p < 0.01). CTCs per 7.5 mL DLA product were median 9.2 times (interquartile range = 5.6-24.0) higher than CTCs in 7.5 mL blood. RosetteSEP did not significantly improve CTC detection (pretreatment: 34/55, 62%, post treatment: 16/34, 47%) and CTCs per mL even decreased compared to DLA (p = 0.04). Patients with advanced-stage disease with DLA-CTC after treatment showed fewer tumour responses and shorter progression-free survival (PFS) than those without DLA-CTC (median PFS, 2.0 vs 12.0 months, p < 0.01). DLA-CTC persistence after treatment was independent of clinical factors associated with shorter PFS (hazard ratio (HR) = 5.8, 95% confidence interval (CI), 1.4-35.5, p = 0.02). All evaluable CTCs showed aneuploidy.

DLA detected nine times more CTCs than in the peripheral blood. The sustained presence of CTCs in DLA after treatment was associated with therapy failure and shortened PFS.

The study was approved by the Medical Ethical Committee (NL55754.042.15) and was registered in the Dutch trial register (NL5423).