Efficacy and Tolerance of Cladribine for Non‐Langerhans Cell Histiocytosis

Background Erdheim‐Chester Disease ( ECD ) and Rosai‐Dorfman Disease ( RDD ) Are Rare Non‐Langerhans Cell Histiocytoses That Share Several Clinical and Histological Features, Including the Accumulation of CD1a ‐ Histiocytes in Organs. Cladribine, a Purine Analog, Leads to an Overall Response Rate ( ORR ) of 91% in Langerhans‐Cell Histiocytoses. Whether the Same Results Could Be Obtained in Non‐Langerhans Cell Histiocytoses Remains To Be Determined. Patients and Methods We retrospectively assessed the efficacy of cladribine according to clinical and radiological responses in consecutive patients with a diagnosis of ECD, RDD, or non‐classified non‐Langerhans cell histiocytosis. Results Twenty‐One Patients Were Included in This Study (17 Males, Median Age at Cladribine Treatment 53 Years). The Clinical ORR Was 62% (44% in ECD , 70% in RDD ), whereas the Radiological ORR Was 43% (44% in ECD , 30% in RDD ). Four of Five Patients With Cranial Nerve Palsy Responded Clinically (80%), whereas Pseudo‐Degenerative CNS Involvement Did Not Improve ( n = 3). Six Patients With Multisystemic Involvement Did Not Require Additional Treatment After Achieving a Radiological Response ( n = 4) or After Achieving Radiological Stable Disease ( n = 2), with a Median Follow‐Up of 2.3 Years (Range 0.5–9.5). After They Achieved a Radiological Response, 4/9 (44%) Patients Relapsed in a Median Time of 18 Months (Range 6–95). The Safety Profile Showed That 19/19 Patients Experienced Lymphopenia, Whereas Only 2/19 Had Clinical Infectious Events (9%). Conclusions These Results Provide New Evidence of the Efficacy of Cladribine in Non‐Langerhans Cell Histiocytosis and Brings New Data on the Safety Profile of This Drug in Histiocytoses.