Undifferentiated malignant neoplasms of the sinonasal tract

The most commonly encountered malignant neoplasms of the sinonasal tract are the keratinizing and nonkeratinizing types of squamous cell carcinoma. However, this complex anatomic region may represent the site of aggressive, non-squamous cell epithelial and nonepithelial malignant neoplasms of varying histogenesis, which are grouped under the term undifferentiated malignant neoplasms. Frequently, these undifferentiated malignancies share clinical and light microscopic features, which makes differentiation of one from the other virtually impossible without the use of adjunct analyses (eg, immunohistochemistry, electron microscopy, or molecular biologic studies). These tumors often are clinically aggressive and usually fatal, despite all attempts at controlling disease. Nevertheless, differentiating these tumors has clinical import because advances in therapeutic intervention may increase survival with good quality of life, and in some instances may achieve a cure. To compare and contrast the clinical, light microscopic, and immunohistochemical features of sinonasal undifferentiated malignant neoplasms. Case-derived material and literature review. A variety of undifferentiated malignant neoplasms occur in the sinonasal tract with overlapping clinical and pathologic findings. In limited biopsy material, differentiation of these tumor types can be challenging. The pathologist plays a primary role in establishing the correct diagnosis, which often necessitates the use of adjunct studies that allow for differentiating among these neoplasms.