INSM1 expression in primary and metastatic neuroendocrine neoplasms at distinct locations

Insulinoma-associated protein 1 (INSM1) has been reported as a valuable marker for neuroendocrine neoplasms (NENs). The aims of this study were to evaluate any change in INSM1 expression between primary and metastatic NENs in distinct locations, as well as the expression of INSM1 at different differentiation levels. Furthermore, we would also investigate the significance of INSM1 expression in non-neuroendocrine neoplasms (non-NENs).We collected 78 cases with primary NENs and 16 cases with metastatic NENs. An addition 7 cases of non-NENs with neuroendocrine (NE) differentiation and 84 cases of other non-NENs, respectively, were included as controls.In our cohort, 82% of primary NENs and 88% of metastatic NENs expressed INSM1 with no difference between them. There was no difference in the expression of INSM1 in the lung and digestive system, and its staining pattern was independent of tumor differentiation or location. The proportion of INSM1 -positive in non-NENs with NE differentiation was significantly higher than that in other non-NENs. INSM1 sensitivity for primary NENs (82%) was comparable to Chromogranin A (82%), less than that of Synaptophysin (96%) and CD56 (94%); specificity was higher (96% vs 94%, 82%, and 89%, respectively). The sensitivity of INSM1 for well differentiated NENs was significantly higher than that of poorly differentiated NENs (100% vs 79%).INSM1 is a useful neuroendocrine marker in primary and metastatic NENs, helping to identify primary NENs with different degrees of differentiation. The expression of INSM1 was independent of tumor location. It should be with caution to interpret the expression of INSM1 in non-NENs that morphologically resemble NENs.