Long‐term follow‐up of children with risk organ‐negative Langerhans cell histiocytosis after 2‐chlorodeoxyadenosine treatment

Summary The nucleoside analogue, 2‐chlorodeoxyadenosine (2CDA), was reported to be an active treatment for childhood Langerhans cell histiocytosis (LCH) without risk organ (RO−) involvement. However, we lack data on long‐term effects of 2CDA treatment, including the disease reactivation rate, permanent sequelae and long‐term tolerance. This study included 44 children from the French LCH registry, treated for a RO− LCH with 2CDA monotherapy (median number of six courses). The median age at the beginning of 2CDA was 3·6 years (range, 0·3–19·7 years) and the median follow‐up after was 5·4 years (range, 0·6–15·1 years). Objective response to 2CDA was observed in 25 patients (56·8%), while six patients (13·6%) had stable disease and 13 patients (29·5%) exhibited progressive disease. Among patients without progression, only two experienced disease reactivation after 2CDA discontinuation. The five‐year cumulative incidence of disease progression or reactivation after 2CDA therapy initiation was 34·3%. The lymphopenia reported in all cases [72% below absolute lymphocyte count (ALC) of 0·5 G/l], was addressed with appropriate prophylactic measures. Other toxicities above grade 2 were uncommon, and no second malignant neoplasm or neuropathy was reported. The five‐year overall survival was 97·7%. In conclusion, we could confirm that 2CDA monotherapy was a beneficial long‐term therapy for treating patients with RO− LCH. Appropriate management of induced immune deficiency is mandatory.