Rationale: Extramedullary invasion of chronic myelomonocytic leukemia (CMML) usually occurs in the liver, spleen, and lymph nodes, while the pleural infiltration of CMML is rare. The presence of pleural effusion is usually associated with uncontrolled leukocytosis and increased monocytes.
Patient concerns: Here we reported a rare case of CMML-0 with pleural effusion as the first manifestation in a 44-year-old woman. The pleural effusion was caused by blasts infiltration confirmed by the flow cytometer and the pleural biopsy.
Diagnoses: CMML with pleural invasion.
Interventions: The patient was treated with azacitidine 75 mg/m d for 2 cycles, followed by daily oral intake of hydroxyurea (500 mg/d).
Outcomes: Pleural effusion was resolved and chest pain was relieved.
Lessons: The current case indicated that leukemic infiltration into pleura could occur despite mild leukocytes, while demethylation may be an effective therapy.