Granulomatous inflammation-an underestimated cause of false-positive diagnoses in lung fine-needle aspirates: observations from the college of american pathologists nongynecologic cytopathology interlaboratory comparison program.
BACKGROUND
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.


METHODS
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%.


CONCLUSIONS
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.
Department of Pathology, McGill University Health Center, McGill University, Montreal, Quebec, Canada. manon.auger@mcgill.ca
Manon
M
Auger
Ann T
AT
Moriarty
Rodolfo
R
Laucirica
Rhona
R
Souers
Beth Anne
BA
Chmara
Lisa A
LA
Fatheree
David C
DC
Wilbur
D044963:Biopsy, Fine-Needle / Q000592:standards; D018288:Carcinoma, Small Cell / Q000175:diagnosis*; D003581:Cytodiagnosis / Q000379:methods / Q000592:standards; D003937:Diagnosis, Differential; D005189:False Positive Reactions; D006099:Granuloma / Q000175:diagnosis*; D006801:Humans; D008175:Lung Neoplasms / Q000175:diagnosis*; D011014:Pneumonia / Q000175:diagnosis*; D011237:Predictive Value of Tests; D012189:Retrospective Studies