Inclusion Criteria:  Patient under 18 years of age at the time of inclusion. Histopatologically confirmed or suspected histiocytosis (based on prior test results). Signing of informed consent for trial participation according with current legal regulations.  Exclusion Criteria:  Lack of inclusion criteria. Pregnancy. Other acute or persistent disorders, behaviors or abnormal laboratory test results, which might increase the risk related to the participation in this clinical trial or to taking the study drug, or which might influence the interpretation of the study results, or which, in the investigator's opinion, disqualify a patient from participating in the trial.