Sequential Development of Chronic Lymphocytic Leukemia (CLL) in a Chronic Myeloid Leukemia (CML) Patient Treated With Nilotinib: A Case Report.

Chronic myeloid leukemia (CML) and chronic lymphocytic leukemia (CLL) are distinct clonal hematologic malignancies that rarely occur in the same patient. We report the case of a 52-year-old male with CML who achieved a sustained major molecular response on the tyrosine kinase inhibitor (TKI) nilotinib and who subsequently developed asymptomatic CLL during follow-up. The CML was well-controlled (BCR-ABL1 < 0.1%), and leukocytosis was investigated and found to be due to a monoclonal B-cell population consistent with CLL. This unusual sequential presentation highlights the importance of evaluating unexplained leukocytosis even in a patient with well-managed CML. We discuss potential pathophysiologic mechanisms, including whether TKI therapy could influence clonal evolution and review relevant literature. The patient continues nilotinib therapy with ongoing CML remission and remains under observation for CLL, underscoring a conservative management approach given the indolent nature of his CLL. This case adds to the sparse literature on CML and CLL co-occurrence and raises awareness of secondary hematologic malignancies in TKI-treated CML patients.