MYC Negative Rectal B-Cell Lymphoma, Unclassifiable, with Features Intermediate between Diffuse Large B-Cell Lymphoma and Burkitt’s Lymphoma in an Immunocompetent Patient

B-cell lymphoma, unclassifiable, with features intermediate between diffuse large B-cell lymphoma and Burkitt’s lymphoma (BLUI) is a recently added entity to the World Health Organization (WHO) classification to address a grey zone between large B-cell lymphoma (DLBCL) and Burkitt’s lymphoma (BL). These are rare aggressive lymphomas, which were previously also known as Burkitt’s-like lymphoma (BLL). BL and BLUI/BLL of the colon mostly involve the ileocecal region. In the rectum, BL and BLUI/BLL almost always affect patients with the acquired immune deficiency syndrome (AIDS). We report the first case of rectal BLUI/BLL in an immunocompetent patient who is also negative for MYC abnormalities and the EBV early RNA (EBER) in situ hybridization. 1. Introduction The border between classical Burkitt’s lymphoma (BL) and classical diffuse large B-cell lymphoma (DLBCL) has been a field of diagnostic uncertainty [1]. The updated WHO classification of tumors of the hematopoietic and lymphoid tissues described these borderline lymphomas as “lymphoma, unclassifiable, with features intermediate between DLBCL and BL” (BLUI) [1]. Rectal BL and BLUI almost always affect patients with the human immunodeficiency virus (HIV) infection [2–4]. To the best of our knowledge, this is the first case of rectal BLUI in an immunocompetent patient who does not reveal MYC abnormalities and is also negative for EBV early RNA (EBER) in situ hybridization. 2. Case Report A sixty-three-year-old heterosexual male with a past history of aortic aneurysm and prostate cancer presented with hematochezia. On examination, a submucosal nodule measuring 6？mm in greatest dimension was noted in the distal rectum about 2？cm from the anal verge. Histopathological examination revealed a monomorphic mucosal lymphoid proliferation with numerous mitotic figures (Figure 1(a)). Nuclear polymorphism was slightly augmented compared to classic BL. The lymphoid cells expressed CD20, CD10, Bcl6 (Figure 1(d), inset), and Ki-67 (~100%, Figure 1(b)) and were negative for CD3, CD5, CD23, and Bcl2 (Figure 1(d)). EBER by in situ hybridization was also negative (Figure 1(c)). There was no morphologic, flow cytometric, or cytogenetic evidence of bone marrow involvement. Serologic tests for human immunodeficiency and hepatitis viruses were also negative. MYC translocations and rearrangement could not be detected by FISH. Based on nuclear pleomorphism and lack of MYC abnormalities, a diagnosis of rectal BLUI was made. Hematopathologists from a referral institute also concurred with this diagnosis. Figure 1: