Epidermotropic neuroendocrine carcinoma. Immunohistochemical differentiation from simulators, including malignant...

Epidermotropic neuroendocrine carcinoma (NEC) is rare. Based on such a case in an 88-year-old woman with a facial NEC showing epidermotropism with a pagetoid growth pattern, we asked whether several similar tumors involving the epidermis could be easily differentiated by immunohistochemical methods. We constructed a panel of control cases (2 each) for NEC, clear cell Bowen's disease (CCBD), Paget's disease (PD), superficial basal cell carcinoma (SBCC), cutaneous T-cell lymphoma (CTTL), and superficial spreading malignant melanoma (SSMM) to compare with our patient. A panel of antibodies including epithelial membrane antigen (EMA), neuron specific enolase (NSE), AE1/3 cytokeratin (CK), carcinoembryonic antigen (CEA), leukocyte common antigen (LCA), S-100, and HMB-45 were applied. Cutaneous NEC controls and our patient's tumor were strongly positive for EMA and NSE and had paranuclear dot-like cytoplasmic positivity for CK. CCBD was moderate to strong for CK. PD was strong for CEA. SBCC was essentially negative for all. CTLL was strong for LCA. SSMM was strong for S-100 and HMB-45. Controls were either negative or weak for the antibodies not mentioned. We conclude that this antibody panel can reliably differentiate these epidermotropic or juxtaepidermal tumors in diagnostic dermatopathology and should be applied to lesions requiring separation beyond H & E capabilities, especially with superficial shave biopsies showing small cell "Pagetoid" growth patterns.