Prospective, low intervention, open, single-center, non-commercial clinical trial to improve diagnostics in patients with histiocytosis by assessing the molecular profile of the tumor tissues, monitoring its presence in free-circulating DNA, and determining the efficacy of fluorodeoxyglucose (18F-FDG) in PET-CT imaging.

HISTIOGEN clinical study is part of the POLHISTIO project. The POLHISTIO project is a non-commercial clinical trial aimed at optimizing the diagnosis and treatment of juvenile patients with histiocytosis. The project objectives are defined as follows: 1) to estimate the nature and frequency of mutations in patients with histiocytosis in both tumor tissues and free-circulating DNA; 2) to compare molecular test results with clinical data; 3) to evaluate the diagnostic usefulness of the status of molecular analysis (MRD) as a prognostic factor compared with other recognized factors. As part of the HISTIOGEN protocol, an immortalized cell line will be derived to study the pathogenesis of the disease, drug sensitivity, and drug resistance mechanisms. The project is intended to include patients from all over Poland

Inclusion Criteria:

1. Patient under 18 years of age at the time of inclusion.
2. Histopathologically confirmed or suspected histiocytosis (based on prior test results).
3. Signing of informed consent for trial participation according with current legal regulations.

Exclusion Criteria:

1. Lack of inclusion criteria.
2. Pregnancy.
3. 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.