Claudia Henschke, MD, PhD
Director, Early Lung & Cardiac Action Program
Professor of Radiology
Mount Sinai Medical Center
New York, NY
In CT screening for lung cancer, the regimen of screening is a critical factor in diagnosing lung cancer early while limiting unnecessary tests and invasive procedures. This has been clearly demonstrated by comparing the results of two studies, one with and one without a well-defined regimen of screening. The study that used a regimen of screening had a significantly higher proportion of stage I lung cancer, the tumor size was smaller, and the frequency with which the cancer could be removed surgically was higher.1
As a result, the cure rate was also significantly higher. Screening is increasingly being reimbursed by insurance carriers based on the US Preventive Services Task Force (USPSTF) report in 2013, which recommends annual screening for high-risk smokers aged 55 to 80.2
Further, the Centers for Medicare & Medicaid Services recently announced that the agency plans to cover low-dose CT screening
for lung cancer in high-risk Medicare patients. It is increasingly being recognized that to maximize the benefit of screening and minimize potential harms, a regimen of screening must be used, and it requires continuous evaluation and updating to remain state-of-the art, incorporating the latest novel technical innovations and emerging screening data. For this purpose, large databases are needed to provide important information on findings that are identified by screening, particularly in annual rounds of screening where the data have previously been sparse.
Early on in CT screening for lung cancer, data from the Early Lung Cancer Action Project (ELCAP)3-6
provided guidance that led to the recommendations for workup of nodules identified as a result of the screening. The expanded International Early Lung Cancer Action Program (I-ELCAP), with more than 31,000 participants who had CT screening, provided further information.7-11
Currently, I-ELCAP has more than 66,000 participants and is using this accumulated evidence to develop the updated guidelines for the workup of findings resulting from CT screening for lung cancer.12,13
It has been previously shown that the frequency of identifying noncalcified nodules—solid and subsolid—and the frequency of diagnosing lung cancer manifesting in such nodules is very different for the first, baseline round of screening when compared with all subsequent rounds of annual repeat screening.3,4,14
Using the latest CT scanners, at least one noncalcified nodule is identified in 50% of baseline screenings but much less frequently (about 7%) in annual repeat screenings. Lung cancer is diagnosed much more frequently in the baseline round than in a single round of annual repeat screening. In the baseline round of screening, the probability of diagnosing lung cancer manifesting as a solid nodule is lower than the probability of diagnosing lung cancer manifesting in a sub-solid nodule. But this is reversed in annual repeat rounds where it is more likely to diagnose a cancer manifesting as a new solid nodule than in a new sub-solid nodule. The difference in the relative frequency of different cell-types in baseline and annual rounds of screening has been described.14
The relative frequency of adenocarcinoma decreases in annual rounds when compared with the baseline round, while it increases for squamous cell and small-cell carcinomas, reflected in the greater aggressiveness of the latter two cell types.
This difference between the baseline and the subsequent annual repeat rounds becomes important when annual rounds of screening are repeated as often as 24 times, according to the USPSTF recommendations for an individual who starts baseline screening at age 55. Unfortunately, these differences were not so apparent in randomized screening trials, such as the National Lung Screening Trial15
as they had only a few rounds of annual repeat screening, and thus the results are dominated by the baseline round.