Lung cancer test less accurate when lung infections prevalent

1. The specificity of FDG-PET imaging for diagnosing lung cancer is significantly reduced in areas endemic to infectious lung diseases.

2. The sensitivity of FDG-PET imaging did not significantly change when studied in areas endemic to infectious lung diseases.

Evidence Rating Level: 3 (Average)

Study Rundown: Currently, positron emission tomography (PET) combined with fluodeoxyglucose F 18 (FDG) is reported to have 94-96% sensitivity and 78-86% specificity in characterizing whether a lung nodule is benign or malignant. This study sought to determine whether this accuracy holds true when there is also an endemic infectious granulomatous lung process present. The results showed that while the sensitivity of the test did not change when used in areas with high prevalence of endemic lung disease, the specificity significantly decreased, making it more difficult to distinguish benign disease from malignancy.

While meta-analyses are useful tools in compiling and analyzing a large amount of data, it is important that the data being analyzed is of good quality and reliable. This meta-analysis included not just randomized controlled trials but also retrospective cohort trials, which increased the heterogeneity of the results. Because of this heterogeneity, it is difficult to make strong predictions based on the results from this study. Nevertheless, the results should caution clinicians to be more aware of the possibility of false positives in endemic areas that adopt low-dose CT as a method for lung cancer screening.

Click to read the study, published today in JAMA

Relevant Reading: Accuracy of Positron Emission Tomography for Diagnosis of Pulmonary Nodules and Mass Lesions – A Meta-analysis

In-Depth [meta-analysis study]: This study was a meta-analysis that used data from published studies between 2000-2014 that evaluated individuals for possible lung cancer via FDG-PET, FDG-PET/CT, or FDG-PET with another imaging modality. Seventy studies were chosen to be eligible to contribute data on 8,511 lung nodules to the meta-analysis. Ten of those studies reported endemic infectious disease. Studies were classified as being from an endemic lung infection area (histoplasmosis, blastomycosis, coccidiomycosis, or tuberculosis) if the study reported presence of infectious lung disease in the patient population recruitment pool or if >50% of benign lung nodules were due to infectious lung disease.

There was significant heterogeneity among the studies in sensitivity and specificity of PET/FDG scan, even after adjusting for study characteristics. Adjusted estimate of sensitivity when taking into account only rigorously conducted and well-controlled studies as decided by the study authors was 96% (95%CI 92-98%) in endemic regions vs. 90% (95%CI 86-93%) in non-endemic regions. For adjusted estimate of specificity, it was 61% (95%CI 49-72%) in endemic regions vs. 77% (95%CI 73-80%) in non-endemic regions. Lung lesions greater than 2 cm had a slightly higher sensitivity with no change in specificity. The type of FDG-PET scan that was used in the study affected the sensitivity in that the studies using FDG-PET/CT had a slightly better sensitivity compared to other types of imaging modalities. Specificity did not change with different imaging FDG-PET modalities.

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