Context: The false-positive rate for fine-needle aspirates of the lung has been cited as less than 1% for granulomatous inflammation, comprising one of the known causes of false-positive diagnoses.
Objective: To determine the rate of false-positive diagnoses of granulomatous inflammation for lung fine-needle aspirates by assessing the false-positive response rate in the context of the College of American Pathologists Nongynecologic Cytopathology Interlaboratory Comparison Program.
Design: We performed a retrospective review of 1092 participant responses for lung fine-needle aspirate challenges with the reference diagnosis of specific infections/granulomatous inflammation from 1998 to 2008 from the College of American Pathologists Nongynecologic Cytopathology Interlaboratory Comparison Program. False-positive rates by participant type (pathologist versus cytotechnologist), general diagnosis category, reference diagnosis, and preparation type were analyzed for the pathologists' responses.
Results: Of the 502 general category responses for pathologists, 428 (85.3%) were benign, 55 (11%) were malignant, and 19 (3.8%) were suspicious. There was no difference in the false-positive rate between preparations (P = .76) or participants (P = .39). Of those responses by pathologists that were benign, only 68.7% (292 of 425) were an exact match to granulomatous inflammation. Non-small cell carcinoma, adenocarcinoma, and squamous carcinoma represented 64% of false-positive/suspicious responses, while small cell carcinoma and carcinoid comprised 13%.
Conclusion: In an interlaboratory comparison program, granulomatous inflammation represents an important cause of false-positive/suspicious responses in lung fine-needle aspirates (14.8%) and is much higher than false-positive rates reported historically in clinical studies. These results highlight the importance of granulomatous inflammation as a mimic of carcinoma.