The multiple faces of carcinoid tumor: performance characteristics of low-grade neuroendocrine carcinoma metastatic to the liver in an educational interlaboratory slide comparison program.

CONTEXT

Cytologic features of low-grade neuroendocrine carcinoma are well described in primary sites. There are fewer reports of the cytologic features specific to metastatic liver lesions or the frequency of misdiagnosis.

OBJECTIVE

To identify discriminating cytologic features and characterize the rate of misdiagnosis of low-grade neuroendocrine tumors metastatic to the liver in an educational interlaboratory slide comparison program.

DESIGN

Glass slides with the specific reference diagnosis of metastatic low-grade neuroendocrine tumor involving liver were circulated to 175 laboratories, with 575 participant responses in the College of American Pathologists Interlaboratory Comparison Program in Nongynecologic Cytology. Eight specific cytologic features were assessed to identify predictors of poor performance (>10% misdiagnosis).

RESULTS

There was an exact match diagnosis in 496 of 575 responses (86%); 555 of 575 responses (96.5%) were correctly identified as malignant. Incorrect responses included adenocarcinoma (27), hepatocellular neoplasm (21), small cell carcinoma (11), benign neoplasm not otherwise specified (6), benign liver (3) and inflammation (3). Three features were significantly associated with the misdiagnosis of adenocarcinoma: presence of large clusters (P = .02), lack of single-cell pattern (P = .02), and lack of stripped nuclei (P = .01).

CONCLUSION

Participants often recognize metastatic low-grade neuroendocrine carcinoma in an educational glass-slide program. Adenocarcinoma was the most common incorrect diagnosis, especially in the presence of large cellular clusters or absence of a single-cell pattern or stripped nuclei.