Clofarabine for relapsed/refractory LCH and non-LC histiocytosis

Langerhans cell histiocytosis (LCH) and non-Langerhans cell (non-LC) histiocytosis are rare neoplastic diseases with variable behavior. Although chemotherapy is often effective, some patients respond poorly to treatment, experience disease recurrence and/or develop long-term complications. Clofarabine (Clolar), a deoxyadenosine analog, has shown encouraging activity in histiocytic disorders. Here, we report a prospective, multicenter, phase 2 study evaluating the efficacy and toxicity of clofarabine in recurrent/refractory (R/R) LCH (stratum 1) and non-LC histiocytosis (stratum 2). All participants received clofarabine on days 1 through 5 of each 28-day cycle. Response was assessed after 2 cycles; participants without evidence of disease progression received 4 additional cycles. A total of 25 participants enrolled: 20 in stratum 1 and 5 in stratum 2. In stratum 1, 17 of 20 participants (85%; 95% confidence interval [CI], 62%-97%) were responders, and 3 had stable disease after cycle 2. Overall, 19 stratum-1 participants completed 6 cycles; 1 withdrew after cycle 3. No stratum-1 participants progressed during treatment and 3 had disease recurrence after cycle 6, resulting in 2-year progression-free survival ± standard error and overall survival of 89% ± 7% and 100%, respectively (n = 20; median follow-up, 40.9 months [range, 2.7-49.4]). In stratum 2, 3 of 4 evaluable participants (75%; 95% CI, 19%-99%) had partial response. Overall, 20 of 25 (80%) of participants had ≥1 grade ≥3 toxicity attributed to protocol therapy. In conclusion, clofarabine is active and tolerable in children with R/R LCH and warrants further study in patients with non-LC histiocytosis. Further study of clofarabine in these populations is warranted. This trial was registered at www.clinicaltrials.gov (#NCT02425904).