Purpose: To determine the proportion of the cancers diagnosed on annual repeat CT screening as compared to those diagnosed on prompting of symptoms in between the annual screenings. Further to determine the stage, cell-type, growth rate of these cancers and the number of deaths due to lung cancer after long-term follow-up.
Methods and Materials: Multiple annual repeat CT screenings were performed on 2,957 high-risk subjects according to our protocol since 1993. A cancer was classified as an annual repeat screen-diagnosis if its diagnosis was prompted by findings on low-dose CT performed 11-13 months after a previously negative screen. A cancer was classified as interim-diagnosis if its diagnosis was prompted by symptoms first appearing within 12 months after a negative result of such an annual repeat screening. Growth rates were determined for all cancers. Follow-up of each case and use of the Kaplan-Meier methodology permitted direct estimation of the cure rate of the fully resected screen-diagnosed cases of lung cancer.
Results: Among the 20 cases diagnosed under annual repeat screening, 19 were screen-diagnosed and 1 was interim-diagnosed. Thus, annual repeat screening produced a high proportion of screen-diagnosed cases (19/20) and among the 19 screen-diagnosed cases, it produced a high proportion of Stage I cases (17/19). Adenocarcinoma represented 60%, non-small-cell carcinoma NOS 10%, squamous-cell carcinoma 10% and small-cell carcinoma 10% of the cases, similar to the distribution in the unscreened population in our catchment area. Volume doubling times consistent with aggressive cancers. No death due to lung cancer occurred to date in those having full resection, while the 2 cases which were not resected died within 3 years of diagnosis.
Conclusion: These results indicate that annual CT screening is sufficiently frequent to commonly produce diagnosis of lung cancer in Stage I and to minimize interim-diagnoses. The cancers were aggressive, not overdiagnosed cases of lung cancer as confirmed by deaths due to lung cancer among the unresected cases. Long-term follow-up of the fully resected cases suggests a high cure rate of screen-diagnosed lung cancers.