The purpose of this study was to assess safety, efficacy and PK in adult Langerhans Cell Histiocytosis (LCH) and Erdheim-Chester Disease (ECD) given HLX208 (BRAF V600E inhibitor).

Inclusion Criteria:

1. Volunteer to participate in the clinical study;
2. Aged ≥ 18 years;
3. Confirmed adult patients with LCH and/or ECD with BRAF V600E mutation;
4. At least one measurable lesion as per PERCIST v1.0;
5. Expected survival time ≥ 3 months;
6. ECOG score 0-2;

Exclusion Criteria:

1. Previous treatment with BRAF inhibitors or MEK inhibitors;
2. A history of other malignancies within two years, except for cured cervical carcinoma in situ, basal cell carcinoma of the skin, adenocarcinoma in situ of the lung, or tumors that do not require interventional treatment after radical surgery;
3. Severe active infections requiring systemic anti-infective therapy;
4. Other anti-tumor treatments, such as chemotherapy, targeted therapy, or radiation therapy (except palliative radiation therapy), may be given during the study period.