Pitfalls in diagnosing a case of extranodal NK/T-cell lymphoma with CD20 aberrant expression and IGH gene rearrangement.

Extranodal NK/T-cell lymphoma (ENKTL) is a subtype of non-Hodgkin lymphoma mainly derived from NK cells and, uncommonly, T-cells. A diagnostic challenge is presented when an atypical phenotype and gene rearrangement are encountered. Herein, we report a case of ENKTL with CD20 expression and IGH gene rearrangement, which is extremely rare. A 57-year-old female patient was seen in 2021 due to a nodule on her left leg and simultaneously impaired eyesight for 6 months. Skin biopsy and immunohistochemistry were performed. The lymphoid cells were positive for CD3, CD56, granzyme B, and TIA-1, partially positive for CD2, and mildly positive for CD20. In situ hybridization for Epstein-Barr virus was positive. Molecular studies revealed immunoglobulin heavy chain (IGH) gene rearrangement, while no T-cell receptor gene rearrangement was detected. The positron emission tomography scan showed that the lymphoma affected bilateral adrenal glands, pelvic cavity, peritoneal cavity, small intestine, skin, and subcutis of the bilateral lower extremities of the patient. Her disease progressed despite eight cycles of chemotherapy and radiation therapy. The importance of this case lies in the atypical phenotype and IGH gene rearrangements, necessitating comprehensive interpretation of clinicopathological data.