Accuracy of Cytology Diagnosis for Well Differentiated Neuroendocrine Tumors: Assessment by the College of American Pathologists Non-Gynecologic Slide Program.

Context.—: The diagnosis and characterization of well-differentiated neuroendocrine tumors (WDNETs) on cytology is challenging, with recognized pitfalls that may have therapeutic and prognostic implications. Objective.—: To analyze data curated by the College of American Pathologists educational slide program for accuracy in the cytologic diagnosis of WDNET. The current state of cytologic diagnosis of WDNET is also reviewed for educational purposes. Design.—: The study cohort included non-gynecologic cytology slides reviewed by participants in the College of American Pathologists Non-Gynecologic Cytopathology Education program. Individual responses for cytotechnologists or cytologists (CT) and pathologists were collated for WDNET. The data were analyzed for concordance with the correct general diagnosis and concordance with the correct reference diagnosis. The exact reference diagnosis available for each site was "pancreatic neuroendocrine tumor," "liver, well/moderately differentiated neuroendocrine tumor," and "lung, well/moderately differentiated neuroendocrine tumor." Performance measures were assessed. Results.—: The WDNET analysis includes 8941 responses from 1382 laboratories. The selection of the general diagnosis of "malignant" or "suspicious for malignancy" was greater than 90% in all body sites. Pathologists correctly identifying WDNET was highest in the pancreas (2501/2738, 91.3%) compared with the lung (805/1019, 79.0%) and liver (1444/1966, 73.4%). Pathologists had better concordance with the diagnosis of WDNET in all sites than CTs (P < .001). Conclusions.—: This large study, encompassing pathologists and CTs, confirms that although participants can identify WDNET on cytology, opportunities for greater accuracy and education persist. The most common incorrect response in the pancreas was adenocarcinoma, while the most common misdiagnosis was small cell carcinoma in the lung and liver.