PAX8 Positivity, Abnormal p53 Expression, and p16 Negativity in a Primary Endometrial Squamous Cell Carcinoma: A Case Report and Review of the Literature

Primary endometrial squamous cell carcinoma (PESCC) is a rare entity. As the clinicopathologic features and the immunophenotype have not been completely defined yet, here we report our experience and review of the literature on this topic. A 73-yr-old nulliparous woman presented with pelvic pain and vaginal bleeding. Endometrial biopsy showed a carcinoma with squamous differentiation infiltrating the myometrium. Total hysterectomy with bilateral salpingo-oophorectomy and selective pelvic lymphadenectomy was performed. Definitive diagnosis was squamous carcinoma of the endometrium, with one lymph node metastasis (stage IIIC1). Immunohistochemistry evidenced immunoreactivity of the tumor cells for cytokeratin 5, p63, cytokeratin 7, PAX8, PTEN, and cyclin D1, aberrant p53 overexpression, and Ki-67 reactivity in ~70% of the tumor cells. Estrogen and progesterone receptor, PAX2, WT1, and p16 were negative. Our case was the first PAX8-positive PESCC in the literature, underlining the Mullerian system origin of this neoplasm. Abnormal p53 expression of this case confirmed its role in the pathogenesis of PESCC. Further studies on a large number of cases are needed to better understand the pathologic features and the immunophenotype of PESCC.