[Clinical and molecular characteristics and prognosis of classical hairy cell leukemia and hairy cell leukemia...

Objective: To evaluate the clinical characteristics, treatment response, and outcomes in patients with classical hairy cell leukemia (cHCL) and HCL variant (HCL-V). Methods: This is a retrospective case series study. Between January 2011 and December 2021, clinical data of 30 patients newly with diagnosed HCL at Peking Union Medical College Hospital were analyzed. The main outcome measures include clinical characteristics, treatment efficacy and survival. The Kaplan-Meier method was used for survival analysis. Results: Twenty-one cases of cHCL and 9 cases of HCL-v were included. The median age at diagnosis was 55.5 (range, 30-86) years, with the ratio of male to female 2.75∶1. The main clinical manifestations included fatigue in 11 cases (36.7%), abdominal distension in 7 cases (23.3%), and infection in 4 cases, while 8 cases were asymptomatic. Splenomegaly was reported in 24 cases (80.0%), including 7 (23.3%) with megalosplenia. The white blood cell count, lymphocyte count, and the proportion of peripheral hairy cells in HCL-v group were significantly higher than those in cHCL group, whereas the development of anemia, thrombocytopenia, and monocytopenia in cHCL group was more remarkable than that in HCL-v group (all P<0.05). The BRAF-V600E gene mutation was detected only in cHCL patients (11/14 vs. 0/9, P<0.001). In terms of immunophenotype, the expression of CD25, CD103, CD123 and CD200 in cHCL group (20/20, 20/20, 4/7, 7/17) were all stronger than those in HCL-v group (3/9, 7/9, 0/4, 2/8). Twenty-two patients were treated, of which 13 cases (12 cases of cHCL and 1 case of HCL-v) with cladribine, and 9 cases (4 cHCL and 5 HCL-v) with interferon. Complete remission rate and overall response rate were comparable between cladribine and interferon treatment groups (both P<0.05). The median follow-up time was 31 (range, 1-125) months, and the median overall survival (OS) of the entire group was 125 months. The 5-year OS rate in HCL-v patients represented a trend of inferior (50.0% vs. 95.0%, P=0.207). Conclusions: The clinical features of HCL are unspecific, which includes fatigue, splenomegaly and recurrent infection. The clinical features, immunophenotype, treatment response and prognosis of HCL-v are different from those of cHCL. BRAF-V600E gene mutation is suggested as a key marker for differential diagnosis. Cladribine is recommended as front-line regimen of cHCL patients with satisfactory efficacy and prognosis. Conversely, response and clinical outcome in HCL-v patients still need to be improved.