Background: Sinonasal tumours are characterized by low incidence, non specific symptoms, and late presentation. Aggressive, nonsquamous cell epithelial and nonepithelial malignant neoplasms of varying histogenesis occurring in sinonasal region are grouped under the term undifferentiated malignant neoplasms. Frequently, these undifferentiated malignancies share clinical and light microscopic features, which make differentiation of one from the other virtually impossible without the use of adjunct immunohistochemical analysis .Methods: Undifferentiated malignant sinonasal tumors biopsied or surgically excised over a period of 5 years were studied. Result:We encountered 22 cases of undifferentiated malignant sinonasal tumors with an incidence of 0.05%, with a mean age of 41 to 50 years and the male to female ratio was 2.1:1. Epithelial tumors (18 cases) constituting 81.82 % predominated over non epithelial tumors (4 cases) constituting 18.18% with a ratio of 4.5:1. 16 tumors involved the nasal cavity (72.7%) and 6 involved paranasal sinuses (27.3%). The most common clinical presentation was mass in the nose 19 cases (86.36%). The most common Undifferentiated malignant tumor encountered was Sinonasal undifferentiated carcinoma-10 cases (45.45%). Conclusion: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 and differentiating these tumors with the help of immunohistoochemistry has clinical importance because advances in therapeutic intervention may increase survival with good quality of life, and in some instances may achieve a cure. Keywords

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