Lung Cancer Screening: Simulations of Effects of Imperfect Detection on Temporal Dynamics

Lung cancer screening intervals based on cancer risk

OBJECTIVES

As low-dose CT screening is gaining acceptance, focus is on increasing the efficiency of screening. One major consideration is to reduce the total number of annual rounds by increasing the interval between screening rounds. It has been suggested that longer intervals could be used for individuals who are at lower risk of lung cancer. In this study, we explored whether eligible participants in a program of LDCT screening who are at lower risk of lung cancer have less aggressive cancers than those at higher risk.

METHODS

We retrospectively identified 118 participants in I-ELCAP database between 1992-2019 who had been screened using HIPAA-compliant protocols and had solid lung cancers diagnosed on an annual round of screening, 7-18 months after the prior round. Volume doubling time (VDT) for each cancer was calculated. Estimated risk of developing lung cancer was calculated using PLCO_M2012 model. The strength of the relationship between VDT and individual PLCO_M2012 scores was assessed by Pearson(r) and Spearman (ρ) correlation coefficients.

RESULTS

VDTs were significantly different by cell-type (p < 0.0001); median VDT for small cell was 34.0 days, followed by other cell-types (61.8 days), squamous-cell (73.3 days), and adenocarcinoma (135.7 days). The median VDT for the 78 (66.1 %) Stage I lung cancers was significantly longer than the 40 Stage II + lung cancers (101.4 days vs. 45.5 days, p < 0.0001). None of the established lung cancer risk indicators (age, pack-years of smoking, or PLCO_M2012 scores) were significant predictors of VDT or lung cancer stage.

CONCLUSION

No significant relationship was demonstrated between risk of developing lung cancer (measured by risk models, age or smoking history) and lung cancer aggressiveness (measured by VDT, cell-type and Stage). This suggests that there is no evidence for determining intervals between repeat screenings using risk-based characteristics. It does not, however, exclude the possibility that future models may establish such a relationship.

Screening for Lung Cancer

BACKGROUND

Lung cancer typically exhibits symptoms only after the disease has spread, making cure unlikely. Because early-stage disease can be successfully treated, a screening technique that can detect lung cancer before it has spread might be useful in decreasing lung cancer mortality.

OBJECTIVES

In this article, we review the evidence for and against screening for lung cancer with low-dose CT and offer recommendations regarding its usefulness for asymptomatic patients with no history of cancer.

RESULTS

Studies of lung cancer screening with chest radiograph and sputum cytology have failed to demonstrate that screening lowers lung cancer mortality rates. Published studies of newer screening technologies such as low-dose CT and "biomarker" screening report primarily on lung cancer detection rates and do not present sufficient data to determine whether the newer technologies will benefit or harm. Although researchers are conducting randomized trials of low-dose CT, results will not be available for several years. In the meantime, cost-effectiveness analyses and studies of nodule growth are considering practical questions but producing inconsistent findings.

CONCLUSIONS

For high-risk populations, no screening modality has been shown to alter mortality outcomes. We recommend that individuals undergo screening only when it is administered as a component of a well-designed clinical trial with appropriate human subjects' protections.

Imaging strategies to reduce the risk of radiation in CT studies, including selective substitution with MRI

"When one admits that nothing is certain one must, I think, also admit that some things are much more nearly certain than others." Bertrand Russell (1872-1970) Computed tomography (CT) is one of the largest contributors to man-made radiation doses in medical populations. CT currently accounts for over 60 million examinations in the United States, and its use continues to grow rapidly. The principal concern regarding radiation exposure is that the subject may develop malignancies. For this systematic review we searched journal publications in MEDLINE (1966-2006) using the terms "CT," "ionizing radiation," "cancer risks," "MRI," and "patient safety." We also searched major reports issued from governmental U.S. and world health-related agencies. Many studies have shown that organ doses associated with routine diagnostic CT scans are similar to the low-dose range of radiation received by atomic-bomb survivors. The FDA estimates that a CT examination with an effective dose of 10 mSv may be associated with an increased chance of developing fatal cancer for approximately one patient in 2000, whereas the BEIR VII lifetime risk model predicts that with the same low-dose radiation, approximately one individual in 1000 will develop cancer. There are uncertainties in the current radiation risk estimates, especially at the lower dose levels encountered in CT. To address what should be done to ensure patient safety, in this review we discuss the "as low as reasonably achievable" (ALARA) principle, and the use of MRI as an alternative to CT.

An Update of CT Screening for Lung Cancer

Currently available results on CT screening for lung cancer show that 1) the work-up on baseline screening can be confined to less than 15% of the individuals and to less than 6% on annual repeat screening, 2) almost all cases are detected by screening with very few diagnoses made between screening on the prompting of symptoms, and 3) over 80% of all the diagnoses are of Stage I. This diagnostic performance results from following the I-ELCAP regimen of screening which defines a positive result of the initial CT in the regimen as well as the work-up leading to a diagnosis of lung cancer. The diagnostic performance raises prognostic questions as to the genuineness and curability of these screen-diagnosed lung cancers. All diagnoses of malignancy were confirmed by an expert pathology review and found to represent genuine lung cancer as defined by the 2004 World Health Organization pathologic criteria. Estimates based on growth rates suggest that about 90% of the baseline-diagnosed Stage I cancers are genuine cancers as are essentially all of those diagnosed on annual repeat screening. Preliminary results of the curability of genuine screen-diagnosed Stage I lung cancers indicate a high curability rate of more than 90%. This suggests that more than a high proportion of deaths from lung cancer can be prevented by CT screening followed by early resection.