The Expression of Neuroendocrine Markers in a Small Subset of Ameloblastoma with Implications of Clusterin

Immunohistochemically, ameloblastomas often express CD56; however, novel neuroendocrine markers such as synaptophysin (SYP), insulinoma-associated protein 1 (INSM1), and chromogranin A (CgA) remain unexplored. We analyzed 36 ameloblastoma specimens for CD56, SYP, CgA, and clusterin (CLU) and examined limited samples for INSM1 expression by performing immunohistochemistry, transmission electron microscopy, and reverse transcriptase-polymerase chain reaction. Our findings indicate that the limited cells were positive for CD56, SYP, CgA, INSM1, and CLU expression in 72% (26/36), 14% (5/36), 0% (0/40), 80% (4/5), and 22% (8/36) of the cases, respectively. CD56 expression correlated with older age, but not with subtype, SYP, and CLU expression. However, SYP-positive cases were exclusively found in CD56- and CLU-positive cases, and SYP and CLU expression were significantly correlated. Selected cases had dense-core granules and <i>NCAM1</i> and <i>SYP</i> mRNA expression. This study is the first to suggest neuroendocrine differentiation in ameloblastomas, as indicated by SYP and INSM1 immunoexpression and the presence of dense-core granules, which are consistent with the recent World Health Organization classification of Head and Neck Tumors guidelines. SYP-positive and CgA-negative phenotypes may characterize neuroendocrine differentiation in ameloblastoma. Although the underlying molecular mechanism remains unclear, CLU expression may be associated with neuroendocrine differentiation.