Stable Long-Term Risk of Leukemia in Patients with Severe Congenital Neutropenia Maintained On G-CSF Therapy.

G-CSF therapy reduces sepsis mortality in patients with severe congenital neutropenia (SCN), but effective therapy has revealed a high syndromic predisposition to myelodysplastic syndrome and acute myeloid leukemia (MDS/AML), particularly in patients who require higher doses of G-CSF. Although the long-term risk of MDS/AML after 10 or more years on therapy remains uncertain, prior data on the limited number of patients with long-term follow-up suggested the hazard rate might be as high as 8%/year after 12 years on G-CSF.

We updated prospective follow-up of 374 well-characterized patients with SCN on long-term G-CSF enrolled in the Severe Chronic Neutropenia International Registry (Blood. 2006 Jun 15; 107(12):4628-35). We ascertained event-free time, deaths from sepsis, and MDS/AML events that accrued since our previous report. Follow-up was censored for patients who received a bone marrow transplant.

The update yielded 3590 person-years of follow-up versus 2043 in the prior report; among patients treated for 10 or more years, there were 849 person-years versus just 67 previously. In all, there were 61 MDS/AML events and 29 deaths from sepsis, versus prior totals of 44 and 19, respectively. After including up-to-date follow-up, the estimated annual hazard of death from sepsis remained qualitatively stable, at 0.81%/year (95% Confidence Interval, CI: 0.56 – 1.16%/year). Similarly, during the first five years after the start of G-CSF therapy, the updated estimate of the hazard curve for MDS/AML showed the same increasing trend as the previous estimate. However, in contrast to the prior estimate that showed a subsequent increasing trend over time (with a large margin of error), the updated hazard curve attained a plateau: after 10 years on G-CSF, the estimated hazard of MDS/AML was 2.3%/year (95% CI: 1.7 – 2.9%/year). Although this aspect of the natural history appears less dire than first suggested, after 15 years on G-CSF, the cumulative incidence was 10% (95% CI: 6 – 14%) for death from sepsis and 22% (95% CI: 17 – 28%) for MDS/AML. Furthermore, for the subset of patients who failed to achieve at 6 months an absolute neutrophil count at or above the median value for the cohort (2188 cells/μL) despite doses of G-CSF at or above the median (8 μg/kg/day), the cumulative incidence after 15 years on G-CSF was 18% (95% CI: 7 – 28%) for death from sepsis and 34% (95% CI: 21 – 47%) for MDS/AML. With additional follow-up, the association of G-CSF dose at 6 months with the relative hazard of MDS/AML became more strongly statistically significant (P = 0.003 versus P = 0.024; the hazard of MDS/AML increased by 1.24-fold (95% CI: 1.08-1.43-fold) per doubling of the dose of G-CSF).

For SCN patients maintained on G-CSF therapy, the hazard of MDS/AML over the long-term falls significantly below the range suggested by preliminary data. The updated hazard estimate of 2.3%/year after 10 years on G-CSF (which includes both MDS and AML events) is similar to that for other inherited bone marrow failure syndromes with a high intrinsic risk of AML, notably Fanconi anemia and dyskeratosis congenita. Nonetheless, the cumulative incidence of both MDS/AML and sepsis death rises to very high levels, and the data continue to support the hypothesis that SCN patients with higher G-CSF requirements are also at higher risk of leukemia.

Boxer:Amgen Inc.: Equity Ownership. Dale:Amgen Inc.: Consultancy, Honoraria, Research Funding, Speaker.