The cytologic diagnosis of "atypical": Criteria and controversies

Historically, the word "atypia" has been applied as a descriptor for cytomorphologic changes that deviate from what is expected; the assessment of deviant vs. expected cytomorphology is in the eye of the beholder. "Atypia" has been used to define a spectrum of changes which includes reactive changes known to be benign, but also for those concerning for malignancy, as well as everything in-between. The absence of a standardized reporting system and/or the lack of communication with clinicians can lead to the overutilization of the atypical category. When faced with a high rate of atypical diagnoses, clinicians are unable to distinguish patients who need more aggressive follow up from those that do not. Patients accessing their test results may not understand what an "atypical" diagnosis means; this can lead to unnecessary patient anxiety. Finally, atypical diagnoses can trigger reflex ancillary testing. This impacts ancillary test performance, as performance depends upon the pre-test probability of the cohort being tested. The inappropriate testing of low-risk patients can result in an increased number of false positive tests, which in turn lead to unnecessary procedures. Given these challenges, we present this special issue on "atypical" diagnoses in the field of cytopathology. In this issue, experts in various areas of cytopathology review the literature and discuss the diagnostic dilemmas of rendering "atypical" cytologic diagnosis, associated controversies, the effect on patient management, and abuse of ancillary studies. This issue also includes brief commentaries from clinicians from four different medical specialties who often encounter indeterminate cytologic diagnoses.