Large-cell neuroendocrine carcinoma without immunohistological positivity or serum elevation of CEA until relapse

We herein report a case of large cell neuroendocrine carcinoma (LCNEC) originating in the right lung upper lobe and showing unique features at relapse in the right middle lobe. The relapsed tumor pathology included a carcinoembryonic antigen (CEA)-positive mantle component and a CEA-negative core area. The latter showed the same pathological picture as the original tumor, both histologically and immunohistochemically. The serum CEA concentration did not increase until the tumor relapsed, and it fell to within the normal range after resection of the relapsed tumor. Rarely, a newly elevated tumor marker suggests relapse, even in resected cases with a negative immunohistochemical study for the marker.