False-positive interpretations of carcinoma in exfoliative respiratory cytology : report of two cases and a review of underlying disorders

The false-positive interpretation of malignancy is a potential pitfall of exfoliative respiratory tract cytopathology. However, the underlying causes of this problem are still relatively under-recognized. The authors herein present two additional examples in which bronchial brushing and washing specimens were misinterpreted as showing carcinoma of the lung. The first case concerned a patient with a granulomatous mass that simulated a malignancy on chest radiographs and was the apparent cause of atypical bronchial squamous metaplasia (ABSM). Exfoliated cells from the latter process were thought to explain the false-positive cytologic result in that instance. In the second case, a large-cell angiocentric T-cell lymphoma replaced the lower lobe of the left lung. It was likewise associated with ABSM as the cause of a mistaken diagnosis of carcinoma in exfoliative respiratory cytology specimens, representing the first instance of such an association of which the authors are aware. Repeated evaluation of all bronchial cytology samples by several experienced pathologists yielded no reliable observations that might have been used to avoid an erroneous interpretation in either case. A review is provided of the spectrum of underlying conditions that may be associated with false-positive respiratory cytology results.