Most tumors were either small-cell or mixed-cell carcinomas, harbored a very high proliferative index (>90%), expressed prototypical neuroendocrine markers such as synaptophysin and/or chromogranin and presented with locally advanced or metastatic disease, developing, in descending order, from major and minor salivary glands, sinonasal structures and the larynx, all these concordant with prior reports (Table 5 summarizes the most relevant studies conducted to date in HN NECs) [1,3,4,7,12,13,14,15,16,17,18,19,20,21,22]. This evidence concerns the gene SYP and metastatic neoplasm.