Impact of concurrent autoimmune conditions on clinical outcomes and leukaemic transformation in chronic myelomonocytic leukaemia

Aims: Chronic myelomonocytic leukaemia (CMML) is a rare overlap syndrome between myelodysplastic neoplasms and myeloproliferative neoplasms. One distinct associated condition is systemic inflammatory and autoimmune disorders (SIADs). Methods: We conducted a retrospective cohort study of newly diagnosed CMML patients at our institution between January 2006 and December 2020, comparing those with and without SIADs. Clinical characteristics, laboratory findings, molecular profiles, survival outcomes and leukaemic transformation rates were analysed. Results: A total of 108 patients were included, of whom 26.9% had SIADs. Immune cytopenia was the most common SIAD, with 51.7% diagnosed concurrently with CMML. Most patients (93.5%) were classified as CMML-1, and 61.1% had the myeloproliferative phenotype. The most frequent mutation was TET2 (25.0%). Patients with SIADs showed a trend toward lower frequencies of ASXL1 (p=0.078) and NRAS (p=0.080) mutations. The median overall survival (OS) was 14.1 months, with a 1-year survival rate of 54%. The 1-year cumulative incidence of leukaemic transformation was 19.3%, and the 1-year leukaemia-free survival (LFS) rate was 49%. Patients with SIADs showed a trend towards longer OS (32.7 vs 9.9 months; p=0.058) and a significantly better LFS (32.7 vs 8.1 months; p=0.017). After adjusting for ASXL1 and NRAS mutations and haemoglobin <10 g/dL, SIADs remained protective against leukaemic transformation (HR, 0.13; p=0.038). Conclusions: SIADs occur in a substantial subset of CMML patients and are associated with significantly better LFS and reduced risk of leukaemic transformation, with a trend towards improved OS. Trial registration number: TCTR20210810003.