A pooled analysis combining 32 observational studies found serum thymidine kinase 1 (TK1) protein levels rise across the spectrum from tumor-free individuals to lung cancer patients, suggesting utility for lung cancer risk assessment. The analysis reported model discrimination with an area under the curve of 0.85 in multivariate approaches, supporting TK1 as a potential blood-based marker for earlier risk stratification. Because the underlying evidence is observational, clinical integration would still require prospective validation and determination of how the marker performs in screening-like settings versus diagnostic workflows.