Sequential Coexistence of Small Lymphocytic Lymphoma as a Second Primary Tumor and BCR:: ABL1-Positive Chronic Myeloid Leukemia: A Case Report

Abstract

Introduction: The simultaneous or sequential occurrence of hematologic malignancies derived from divergent cellular lineages (myeloid and lymphoid) represents an extremely rare clinical and immunobiological phenomenon. The emergence of small lymphocytic lymphoma / chronic lymphocytic leukemia (SLL/CLL) as a metachronous second primary tumor during maintenance therapy and close surveillance of chronic myeloid leukemia (CML) poses a true challenge for differential pathological diagnosis and targeted therapeutic strategies. Objective: To report the diagnostic process, immunohistochemical characterization, and interdisciplinary clinical management of a patient who developed SLL after achieving a deep molecular response for CML under tyrosine kinase inhibitor (TKI) therapy. Case and Methods: A 47-year-old male with an established diagnosis of chronic phase CML with BCR::ABL1 p210 fusion transcript, treated with dasatinib (100 mg daily), achieved a Major Molecular Response. During his 3-year evolutionary surveillance, he developed left supraclavicular and right cervical lymphadenopathies. Neck ultrasound demonstrated rounded nodes with a loss of the corticomedullary relationship. An excisional biopsy of the right cervical lymph node was performed, revealing infiltration by mature monoclonal B lymphoid cells with a CD20+, CD43+, BCL2+, MUM1+ profile, and a Ki67 index of 15%, confirming SLL. During follow-up, the patient developed a pericardial effusion that required the scheduled temporary suspension of the TKI. Conclusions: Sequential myeloid/lymphoid coexistence requires meticulous differentiation between a clonal evolution of a common pluripotential stem cell versus two biologically independent malignancies. Management must be guided by the stratification of IWCLL criteria, individualizing the need for chemoimmunotherapy versus the continuation of TKI therapy.