Tumor Lysis Syndrome Caused by Unrecognized Richter’s Transformation of Chronic Lymphocytic Leukemia: Treatment With Venetoclax for Suspected Disease Progression

Richter’s transformation (RT) is defined as the transition of chronic lymphocytic leukemia (CLL) or small lymphocytic leukemia (SLL) into an aggressive lymphoma. The conversion generally leads to diffuse large B-cell lymphoma (DLBCL), but more aggressive forms such as Hodgkin lymphoma (HL) can also occur. RT is a rare complication of CLL. RT can be confused with CLL progression. Its identification is crucial because the management of lymphoma and CLL differ from each other. Furthermore, the use of certain agents for CLL such as venetoclax increases the risk of tumor lysis syndrome (TLS) in neoplasms with rapid replication such as DLBCL or CLL with hyperleukocytosis (blast crisis). We present the case of a 76-year-old man with a history of CLL on chemotherapy who developed fatigue, malaise, night sweats, chills, and unintentional weight loss for which he was started on treatment with venetoclax due to suspected clinical progression of his disease. The patient developed TLS, requiring hospitalization, and he was found to have an acute blast crisis. Also, his CLL was found to have been transformed into an aggressive DLBCL. This case highlights the importance of differentiating a true progression of CLL from RT into an aggressive lymphoma given that treatment would be different for the two and the prognosis with the transformation is worse.