Prognosis and long‐term outcomes in type I cryoglobulinemia: A multicenter study of 168 patients

Type I cryoglobulinemia (CG) accounts for 10%–15% of all cryoglobulinemias and are exclusively seen in clonal proliferative hematologic conditions. In this multicenter nationwide cohort study, we analyzed the prognosis and long‐term outcomes of 168 patients with type I CG (93 (55.4%) IgM and 75 [44.6%] IgG). Five‐ and 10‐year event‐free survivals (EFS) were 26.5% (95% CI 18.2%–38.4%) and 20.8% (95% CI 13.1%–33.1%), respectively. In multivariable analysis, factors associated with poorer EFS were renal involvement (HR: 2.42, 95% CI 1.41–4.17, p = .001) and IgG type I CG (HR: 1.96, 95% CI 1.13–3.33, p = 0.016), regardless of underlying hematological disorders. IgG type I CG patients had higher cumulative incidence of relapse (94.6% [95% CI 57.8%–99.4%] vs. 56.6% [95% CI 36.6%–72.4%], p = .0002) and death at 10 years (35.8% [19.8%–64.6%] vs. 71.3% [54.0%–94.2%], p = .01) as compared to IgM CG, respectively. Overall, complete response of type I CG at 6 months was 38.7%, with no significant difference between Igs isotypes. In conclusion, renal involvement and IgG CG were identified as independent poor prognostic factors of type I CG.