Sinonasal Undifferentiated and Poorly Differentiated Carcinomas: An Update.

Recent advances have increased our understanding of sinonasal undifferentiated and poorly differentiated carcinomas (UD/PDca). Several novel molecularly defined entities have emerged from within this group. Notably, they have histologic features that overlap with each other, and with other sinonasal neoplasms. Despite molecular advances, sinonasal tumors are primarily characterized based on histologic features, which prompt selected ancillary tests to arrive at the final diagnosis within the spectrum of sinonasal UD/PDca. This review provides insights into their differentiation from each other and from a wide range of more familiar morphologic mimics using immunohistochemistry, in situ hybridization, and molecular testing.