Young investigator challenge: Cadherin-17 and SATB2 in cytology specimens: Do these new immunostains help in differentiating metastatic colorectal adenocarcinoma from adenocarcinomas of other origins?

BACKGROUND Cadherin-17 (intestinal peptide-associated transporter) and SATB2 (SATB homeobox 2) immunoexpression has recently been described in surgical pathology to have value in establishing the colorectal origin of metastatic adenocarcinoma. However, to the authors' knowledge, the role of these markers in metastatic colorectal adenocarcinoma (MCA) in cytology has not been addressed to date. In the current study, the authors evaluated the contribution of cadherin-17 and SATB2 to the diagnosis of MCA in cytology specimens and compared these two novel markers with the standard gastrointestinal immunohistochemistry panel in an attempt to identify the optimal panel. METHODS A total of 43 MCA cytology cases and 68 metastatic noncolorectal adenocarcinoma (non-MCA) cytology controls were stained for SATB2; cadherin-17; and the standard panel of cytokeratin (CK) 7, CK20, and Caudal-Type Homeobox Transcription Factor 2 (CDX2). Staining intensity and percentage of positive cells were recorded. Sensitivity and specificity values for immunostains individually and in combination were computed and compared. RESULTS Despite specificities of 83.8% and 91.2%, respectively, for cadherin-17 and SATB2, when critically examining the new immunostains together with the standard panel, there was no significant difference noted with regard to prediction of MCA (vs non-MCA) compared with the standard panel alone (P