High-grade Undifferentiated Malignant Neoplasm of the Oral Cavity in a Human Immunodeficiency Virus-positive Patient: A Case Report with Review on Immunohistochemistry Panel

Abstract

The term “undifferentiated tumor” describes a diverse collection of neoplasms that, when viewed under standard light microscopy, show little to no signs of cellular differentiation. It represents either a metastasis of unknown origin or a primary neoplasia without an obvious cell line of differentiation. Undifferentiated malignant neoplasm of oral cavity is a rare entity with a very poor prognosis. This report presents the case of a 40-year-old human immunodeficiency virus-positive male with a painless, gradually enlarging mass in the left upper posterior teeth region. Histopathology revealed round-to-ovoid cells exhibiting hyperchromatic nuclei along with prominent nucleoli and atypical mitotic figures. Lesion was confirmed as an undifferentiated malignant tumor by exclusion. All the immunohistochemical markers – lymphoid, melanotic, neuroectodermal, and epithelial lineage – were negative, except for weak focal positivity of CD56 and p16 markers, which did not help clarify the diagnosis. This case emphasizes the need to consider this tumor in the differential diagnosis of head and neck lesions. It also highlights the value of immunohistochemical analysis in reaching a correct diagnosis.