Immunohistochemistry: Thymic carcinoids are immunoreactive for keratins (AE1/AE3, CAM5.2; dot-like pattern) and neuroendocrine markers such as synaptophysin, chromogranin, and NCAM/CD56 (shown here). They may also show focal positivity for hormones such as ACTH, hCG, somatostatin, and calcitonin. TTF-1 is not expressed. Note: NCAM/CD56 is a cell-surface glycoprotein that plays a role in cell-cell adhesion. The staining pattern is cell surface as seen here.