A Study to Determine Safety, Tolerability and Pharmacokinetics of Oral Dabrafenib In Children and Adolescent Subjects

Part 1 was a dose escalation study in subjects with any BRAF V600 mutation-positive solid tumor, designed to optimize efficiency of enrollment, minimize the number of subjects being treated at potentially sub-efficacious dose levels, and incorporating the evolving pharmacokinetic, safety and efficacy data from the adult development program. Dose escalation part of the study was to determine the maximum tolerated dose (MTD) and recommend the dose for phase 2 studies (RP2D). An MTD has not been identified for dabrafenib in the adult population. This does not preclude the identification of an MTD in the pediatric population. Modified RSD was employed to determine the MTD. Part 1 used dual criteria of dose limiting toxicity (DLT) and observed dabrafenib exposures to make decisions to advance to the next dose level. Target exposure criteria based on adults treated at the approved adult dose of 300 mg (150 mg given BID) were observed in this study before meeting criteria for stopping dose escalation due to observations of DLTs, and served as the criteria for determining the RP2D for dabrafenib in pediatric subjects. Thus, MTD has not been established in pediatric population, similar to the previous dose finding efforts in adult subjects.

Part 2 was a tumor specific expansion study to further evaluate the safety/tolerability profile and to discover possible clinical efficacy of dabrafenib in 4 tumor-specific pediatric populations known to have BRAFV600 activation: high grade glioma (HGG), low grade glioma (LGG), Langerhans cell histiocytosis (LCH), miscellaneous tumors including melanoma and papillary thyroid carcinoma (Other). The exposures for subjects dosed on the basis of weight were also evaluated by age categories.

Inclusion criteria

• Written informed consent - a signed informed consent and/or assent (as age appropriate) will be obtained according to institutional guidelines.
• Male or female >=12 months and <18 years of age at the time of signing the informed consent form.
• Recurrent disease, refractory disease, or progressive disease after having received at least one standard therapy for their disease. Note: Subjects with metastatic (and surgically unresectable) melanoma can be enrolled for first-line treatment; Melanoma subjects with CNS involvement may be enrolled.
• At least one evaluable lesion.
• BRAF V600 mutation-positive tumor as confirmed in a Clinical Laboratory Improvement Amendments (CLIA)-approved laboratory or equivalent (the local BRAF testing may be subject to subsequent verification by centralized testing; centralized testing can confirm V600E and V600K mutations only).
• Performance score of >=50% according to the Karnofsky/Lansky performance status scale (subjects with a performance status of <=50% can be enrolled if the subject's confinement to bed and inability to carry out activities is due solely to cancer-related pain, as assessed by the investigator).
• Females of child-bearing potential (with negative serum pregnancy test within 7 days prior to the first dose of study medication) must be willing to practice acceptable methods of birth control .
• Sexually active males, who do not agree to abstinence, must be willing to use a condom during intercourse while taking the study drug, and for 16 weeks after stopping treatment and should not father a child in this period.
• Must have adequate organ function as defined by the following values: Adequate bone marrow function defined as-absolute neutrophil count (ANC) >=1000/ microliter (µL), hemoglobin >=8.0 grams (g)/ deciliter (dL) (may receive red blood cell transfusions), platelets >=75,000/µL (transfusion independent, defined as not receiving platelet transfusions within a 7 day period prior to enrollment).
• Adequate renal and metabolic function defined as: calculated glomerular filtration rate (eGFR) (Schwartz formula), or radioisotope GFR >=90 milliliters/minutes (mL/min)/1.73 meter square (m^2); or a serum creatinine within the institutional reference range upper limit of normal (for age/gender, if available).
• Adequate liver function defined as: bilirubin (sum of conjugated + unconjugated) <=1.5 x upper limit of normal (ULN) for age, aspartate aminotransaminase (AST) and alanine transaminase (ALT) <=2.5 x ULN; AST/ALT may be <5 x ULN at baseline if disease under treatment involves the liver (requires radiographic confirmation of liver involvement).
• Adequate cardiac function defined as: left ventricular ejection fraction (LVEF) of either >=50% by ECHO or greater than institutional lower limit of normal (LLN) by echocardiogram (ECHO) (while not receiving medications for cardiac function), corrected QT using Bazett's (QTcB) interval <450 milliseconds (msecs).

Exclusion criteria

• Part 2 ONLY: Previous treatment with dabrafenib, another RAF inhibitor, or a mitogen-activated protein kinase (MEK) inhibitor (exception: prior treatment with sorafenib is permitted).
• Malignancy OTHER than the BRAF mutant malignancy under study.
• Had chemotherapy or radiotherapy within 3 weeks (or 6 weeks for nitrosoureas or mitomycin C) prior to administration of the first dose of study treatment.
• The subject has received an investigational product within the following time period prior to the first dosing day in the current study: 28 days or 5 half-lives or twice the duration of the biological effect of the investigational product (whichever is warranted by the data).
• History of another malignancy. Exception: (a) Subjects who have been successfully treated and are disease-free for 3 years, (b) a history of completely resected non-melanoma skin cancer, (c) successfully treated in situ carcinoma, (d) CLL in stable remission are eligible.
• Current use of a prohibited medication or herbal preparation or requires any of these medications during the study.
• Unresolved toxicity greater than National Cancer Institute Common Terminology Criteria for Adverse Events (NCI CTCAE) v4.0 Grade 2 or higher from previous anti-cancer therapy, including major surgery except those that in the opinion of the investigator are not clinically relevant given the known safety/toxicity profile of dabrafenib (e.g., alopecia and/or peripheral neuropathy related to platinum or vinca alkaloid based chemotherapy).
• Has leukaemia.
• History of allergic reactions attributed to compounds of similar chemical or biologic composition to dabrafenib and its excipients.
• Autologous or allogeneic stem cell transplant within 3 months prior to enrolment [NOTE: subjects with evidence of active graph versus host disease are excluded].
• History of myocardial infarction, severe or unstable angina, peripheral vascular disease or familial QTc prolongation.
• Subjects with abnormal cardiac valve morphology (>=grade 2) documented by echocardiogram (NOTE: subjects with grade 1 abnormalities [i.e., mild regurgitation/stenosis] can be entered on study).
• Subjects with moderate valvular thickening.
• Known, uncontrolled cardiac arrhythmias (except sinus arrhythmia) within the past 24 weeks
• Uncontrolled medical conditions (e.g., diabetes mellitus, hypertension, liver disease or uncontrolled infection), psychological, familial, sociological, or geographical conditions that do not permit compliance with the protocol; or unwillingness or inability to follow the procedures required in the protocol.
• Presence of active GI disease or other condition (e.g., small bowel or large bowel resection) that will interfere significantly with the absorption of drugs.
• Hepatitis B Virus, or Hepatitis C Virus infection (subjects with laboratory evidence of Hepatitis B Virus clearance may be enrolled).
• Pregnant females as determined by positive human chorionic gonadotropin (hCG) test at screening or prior to dosing.
• Lactating females who are actively breast feeding.