Background Study of the molecular biological characteristics of chronic neutrophilic leukemia complicated with plasma cell disorder (CNL‐PCD) and lymphocytic proliferative disease (CNL‐LPD). Methods The clinical data of a patient with chronic neutrophilic leukemia complicated with monoclonal gammopathy of undetermined significance (CNL‐MGUS) in our hospital were reviewed, and the Chinese and/or English literature about CNL‐PCD and CNL‐LPD in PubMed and the Chinese database CNKI in the past 10 years was searched to analyze the molecular biological characteristics of this disease. Results A 73‐year‐old male had persistent leukocytosis for 18 months. The white blood cell count was 46.77 × 109/L and primarily composed of mature neutrophils; hemoglobin: 77 g/L; platelet count: 189 × 109/L. Serum immunofixation electrophoresis showed IgG‐λ monoclonal M protein. A CT scan showed splenomegaly. Next‐generation sequencing (NGS) showed that CSF3R T618I, ASXL1 and RUNX1 mutations were positive. It was diagnosed as CNL‐MGUS. We summarized 10 cases of CNL‐PCD and 1 case of CNL‐LPD who underwent genetic mutation detection reported in the literature. The CSF3R mutational frequency (7/11, 63.6%) was lower than that of isolated CNL. The ASXL1 mutations were all positive (3/3), which may represent a poor prognostic factor. The SETBP1 mutation may promote the progression of CNL‐PCD. We also found JAK2, RUNX1, NRAS, etc. in CNL‐PCD. Conclusions Chronic neutrophilic leukemia may be more inclined to coexist with plasma cell disorder. The CSF3R mutation in CNL‐PCD is still the most common mutated gene compared with isolated CNL. Mutations in SETBP1 and ASXL1 may be poor prognostic factors for CNL‐PCD.

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