Primary combined neuroendocrine and squamous cell carcinoma of the maxillary sinus: report of a case with immunohistochemical and molecular characterization.

Neuroendocrine neoplasms represent a rare subset of tumors in the sinonasal tract. Combined tumors, with an endocrine and a non-neuroendocrine component, are exceedingly rare, and mainly consist of a combination of neuroendocrine carcinoma with adenocarcinomas. We present the clinico-pathologic and immunohistochemical features of a neuroendocrine carcinoma combined with squamous cell carcinoma, arising in the maxillary sinus. In addition, we evaluated the clonal origin of the two components through analysis of TP53 gene status. Both components were positive for cytokeratins AE1/AE3, while the squamous cell carcinoma was positive for cytokeratin 5/6 and p63, and the neuroendocrine carcinoma showed immunoreactivity for neuron specific enolase, chromogranin, synaptophysin and CD56. In situ hybridization for human papilloma virus and Epstein-Barr virus were negative in both components. A missense mutation in TP53 exon 7 (c.734G>C) and strong nuclear immunostaining for p53 were detected only in the neuroendocrine carcinoma. This suggests that the tumor either derived from one precursor cell with squamous differentiation, which underwent TP53 mutation and acquisition of a neuroendocrine phenotype, or it derived from two separate clones, one with mutated TP53 and neuroendocrine differentiation, and the other with wild type TP53 and squamous differentiation (collision tumor).