Objectives: Differences in results of baseline and subsequent annual repeat rounds provide important information for optimising the regimen of screening.
Methods: A prospective cohort study of 65,374 was reviewed to examine the frequency/percentages of the largest noncalcified nodule (NCN), lung cancer cell types and Kaplan-Meier (K-M) survival rates, separately for baseline and annual rounds.
Results: Of 65,374 baseline screenings, NCNs were identified in 28,279 (43.3%); lung cancer in 737 (1.1%). Of 74,482 annual repeat screenings, new NCNs were identified in 4959 (7%); lung cancer in 179 (0.24%). Only adenocarcinoma was diagnosed in subsolid NCNs. Percentages of lung cancers by cell type were significantly different (p < 0.0001) in the baseline round compared with annual rounds, reflecting length bias, as were the ratios, reflecting lead times. Long-term K-M survival rate was 100% for typical carcinoids and for adenocarcinomas manifesting as subsolid NCNs; 85% (95% CI 81-89%) for adenocarcinoma, 74% (95% CI 63-85%) for squamous cell, 48% (95% CI 34-62%) for small cell. The rank ordering by lead time was the same as the rank ordering by survival rates.
Conclusions: The significant differences in the frequency of NCNs and frequency and aggressiveness of diagnosed cancers in baseline and annual repeat need to be recognised for an optimal regimen of screening.
Key points: • Lung cancer aggressiveness varies considerably by cell type and nodule consistency. • Kaplan-Meier survival rates varied by cell type between 100% and 48%. • The percentages of lung cancers by cell type in screening rounds reflect screening biases. • Rank ordering by cell type survival is consistent with that by lead times. • Empirical evidence provides critical information for the regimen of screening.
Keywords: CT screening; Lead-time bias; Length bias; Solid nodules; Subsolid nodules.