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Risk factors for severe infection in patients with hairy cell leukemia: a long‐term study of 73 patients

Although the survival of patients with hairy cell leukemia (HCL) has been improved by the therapeutic introduction of interferon α and purine analogs, it is still worsened by complications such as severe infections. In this long‐term study, we identified factors influencing patient outcomes in 73 patients with HCL. Median age at diagnosis was 53 yr and the gender ratio (M/F) was 2.3. At the time of HCL diagnosis, 60 patients (82%) were symptomatic and 22 of these had an infection. After a median follow‐up of 13 yr, eight patients had died of secondary cancer (n = 2), HCL progression (n = 1) and age‐related complications (n = 5). The 10‐yr overall survival (OS), progression‐free survival and relapse rates were 91 ± 3%, 14 ± 5% and 87 ± 5%, respectively. In multivariate analyses, age >53 yr was the only factor adversely influencing OS and secondary cancer incidence, with adjusted hazard ratio (HR) of 9.30 (95%CI, 1.15–76.6; P = 0.037) and 2.80 (95%CI, 1.05–7.71; P = 0.04), respectively. Eleven patients developed severe infections. Absolute lymphocyte count (<1 × 109/L) at diagnosis was the only factor influencing the occurrence of severe infections, with an adjusted HR of 4.01 (P = 0.007). Strikingly, we did not observe any significant correlation between neutrophil or monocyte counts and the incidence of infection. We confirmed long‐term survival in HCL but found a high incidence of infection – even late in the course of the disease. The absolute lymphocyte count at diagnosis is a risk factor for the occurrence of severe infections. In addition to careful monitoring of infections, prompt initiation of anti‐HCL treatment should be considered in patients with low lymphocyte counts.