Concurrent CML and MBL in a COPD patient: a case of collision hematologic malignancies and opportunistic infection.

BACKGROUND: Collision hematologic malignancies, characterized by the concurrent presence of clonally independent myeloid and lymphoid neoplasms within a single patient, are exceptionally uncommon. Diagnosing these malignancies is particularly challenging when they occur in the context of chronic inflammatory diseases, where distinguishing between reactive and neoplastic processes is complex. CASE PRESENTATION: We present the case of a 66-years-old male patient with COPD, characterized by a 30 pack-year smoking history, who was admitted due to an acute exacerbation of COPD (AECOPD) accompanied by fever. Notably, despite the complete normalization of C-reactive protein (CRP < 0.2 mg/L), there was a paradoxical increase in the white blood cell (WBC) count to 50.2 × 109/L during treatment with high-dose intravenous methylprednisolone. Concurrently, the absolute lymphocyte count rose to 8.08 × 109/L, a phenomenon we describe as "clinico-laboratory dissociation." This atypical kinetic pattern prompted further hematologic work-up, including bone marrow evaluation, which revealed the coexistence of chronic-phase chronic myeloid leukemia (CML) [BCR::ABL1 IS: 64.93%; t(9;22)(q34;q11.2)] and chronic lymphocytic leukemia (CLL)-like monoclonal B-cell lymphocytosis (MBL) [CD19+CD5+CD23+CD20(dim), κ-restricted, monoclonal IGH rearrangement]. During the diagnostic process, the patient developed life-threatening Pneumocystis jirovecii pneumonia (PJP), confirmed through sputum PCR. The patient received treatment with imatinib (400 mg/day) and high-dose trimethoprim-sulfamethoxazole (TMP-SMX, 15-20 mg/kg/day), resulting in the resolution of respiratory symptoms within 1 week and an early molecular response by day 21, as evidenced by a reduction in BCR::ABL1 IS from 64.93% to 11.03%. CONCLUSION: In this patient with COPD undergoing systemic corticosteroid treatment, steroid-resistant lymphocytosis accompanied by WBC-CRP dissociation led to a bone marrow evaluation that revealed two concurrent clonal hematologic disorders. This single case suggests that such a pattern may warrant hematologic assessment in similar clinical settings, and that even subclinical clonal B-cell disorders may carry immunological relevance meriting further study, though this observation requires validation in larger cohorts before informing clinical practice.