Methods
This was a single-center, prospective study of patients undergoing a curative-intent operation for stage I to IIIA NSCLC (University Hospital of South Manchester, Manchester, UK). Patients with a history of malignancy within 2 years were excluded. Blood samples (10 mL) were taken immediately before surgery from a peripheral vein and intraoperatively (10 mL) from the cancer-draining pulmonary vein before tumor resection or vessel ligation to minimize artifactual elevation in CTC number.5 CellSearch processing and analysis followed previously published protocols.6 and 7 CTC enumeration was expressed as number of cells per 7.5 mL of blood. Circulating tumor microemboli (CTMs) were defined as three or more contiguous CTCs in a cluster.8
Primary and secondary outcome measures were disease-free survival (DFS) and overall survival (OS), respectively. Patients found to have unresectable disease during the operation were not included in the survival analysis. DFS and OS were measured from the day of the operation until either the diagnosis of lung cancer recurrence or death. In patients with no evidence of recurrence, DFS was censored at the date of death or last follow-up. Deaths within 30 days of the operation were not included in the analysis. Peripheral vein CTC status was predefined as positive at one or more CTCs per 7.5 mL of blood.3 Pulmonary vein CTC status was an exploratory end point, and high was defined according to the upper quartile of the CTC count. Kaplan-Meier curves were used to demonstrate DFS and OS for each CTC category and compared using log-rank tests. A Cox proportional hazard regression analysis with a backward conditional regression approach was used to define the optimal multivariate model to determine independent risk factors associated with DFS and OS. Log2 transformation was carried out if nonlinearity was found.
The study was granted ethical approval by the North West 7 Research Ethics Committee (reference no. 10/H1008/79), and all participants gave written informed consent before study participation.