Collision Tumor of the Uterine Corpus: Primary EBV-positive Diffuse Large B-Cell Lymphoma and Endometrioid Carcinoma.

Epstein-Barr virus (EBV)-positive diffuse large B-cell lymphoma (DLBCL) of the uterus is an infrequent entity. Moreover, the coexistence of EBV-positive DLBCL and endometrioid carcinoma in the form of a collision tumor has not been reported in the literature to date. This report details the clinical, histologic, immunohistochemical, and molecular characteristics of a collision tumor consisting of EBV-positive DLBCL and endometrioid carcinoma of the uterine corpus. The patient was a 63-yr-old postmenopausal woman who presented with vaginal bleeding. Ultrasonography detected a 2.3×1.0 cm mildly hyperechoic mass within the uterine corpus. Histologically, the tumor consisted of sheets of medium- to large-sized lymphoid cells intermixed with low-grade endometrioid carcinoma. Immunohistochemically, the neoplastic lymphoid cells exhibited strong CD20 expression, and EBV-encoded small RNA in situ hybridization signals were detected in most of these cells. The endometrioid carcinoma cells strongly expressed estrogen receptor and cytokeratin 18. Molecular analysis revealed clonal rearrangement of the B-cell receptor gene. To the best of our knowledge, no prior cases of collision tumors comprising EBV-positive DLBCL and endometrioid carcinoma have been reported. It is essential to differentiate such collision tumors from endometrioid carcinoma with florid-reactive lymphocytic infiltration and dedifferentiated carcinoma of the uterine corpus. A meticulous analysis of patient's clinical features and of the lesion's histologic, immunophenotypic, and genetic characteristics is necessary for an accurate diagnosis.