What is the prevalence of incidental findings found during lung cancer screening using low dose CT?

Problem

The NHS plan to expand lung cancer screening using low dose computed tomography (LDCT) is likely to reduce deaths from lung cancer. However, it remains unclear whether incidental findings will have a beneficial or detrimental effect upon the screened individual. Coronary artery calcification found incidentally might be used to stratify cardiovascular risk and increase adherence to preventative strategies. Extra-pulmonary malignancy found incidentally might provide an early life-saving diagnosis, while large numbers of false positive findings or over-diagnosis may cause anxiety and harm through investigation and over-treatment. What is the possible effect upon primary and secondary care services? It is not clear from the current literature how many and what type of incidental findings are to be expected from widespread screening. This study intends to estimate the prevalence and type of incidental findings found during LDCT screening for lung cancer using systematic review methodology. This subject is original, with only a single similar review published in 2008, and timely due to the planned expansion of screening in the 2019 NHS long term plan.

Approach

A systematic review of the literature is intended, including all primary lung cancer screening studies that report sufficiently upon the nature and prevalence of the incidental findings found. A full protocol is available on PROSPERO. Two reviewers will independently screen abstracts, full papers for inclusion and quality assess. Data will be extracted using an extraction tool by one reviewer and cross checked. A narrative synthesis will explore themes and heterogeneity. Permitting adequate clinical and methodological homogeneity, fixed and random-effects meta-analysis will be performed to provide pooled estimates with corresponding 95% CIs. Heterogeneity will be assessed by Cochran’s Q test and I2 statistic. Publication bias will be considered using a funnel plot.

Findings

Interim findings suggest significant heterogeneity in the definition of and reporting of incidental findings across studies. It is also clear that incidental findings are numerous. An aggregate of the prevalence for common incidental findings such as coronary artery calcification is expected to show these to be highly prevalent. The prevalence of findings that require further investigation or follow up is expected to be around 10-15% of scans (previously estimated as 14.2%) while the reports of confirmed extra-pulmonary malignancy is generally less than 1%.

Consequences

Estimates of the nature and prevalence of incidental findings can be used to council patients undergoing screening. They can inform further research, guideline development, and policy makers upon the potential benefits and challenges incidental findings pose for primary and secondary care services. The cost of incidental findings has also been omitted from economic modelling and estimates can allow for their inclusion within prevalence-based economic modelling, which might in turn have a significant impact upon overall cost-effectiveness of lung cancer screening.