A Trial of Targeted Therapies for Patients With Slow-Flow or Fast-Flow Vascular Malformations (TARGET-VM)

Inclusion Criteria: Adult or paediatric patient, 2 years of age or over where Body Surface Area (BSA) is greater than or equal to 0.4m2. Patient has a clinical diagnosis of a fast-flow vascular malformation Patient has received standard therapy for the vascular malformation or in which, in the opinion of the investigator, standard therapy is not appropriate - Note: standard therapy may include treatment with sirolimus. A minimum of 14 days since the last dose of sirolimus is required prior to starting treatment with mirdametinib A documented genetic alteration in the RAS-MEK-ERK signalling pathway identified by genetic sequencing prior to enrolment in this study Adequate performance status (Eastern Cooperative Oncology Group Performance Status Scale (ECOG) 0-2 in patients ≥ 16 years of age; Lansky > 50 in patients < 16 years of age) Patient has a life expectancy ≥ 12 weeks Participant has the ability to swallow capsules whole if the capsule dosage form is being utilized. This criterion does not apply if participant is utilizing the dispersible tablet form of study treatment Adequate haematologic and end-organ function: Haematology: Haemoglobin ≥ 9.0 g/dL; Absolute neutrophil count ≥ 1.5 x 109/L; Platelets ≥ 90 x 109/L, except where bleeding leading to low haemoglobin level is an indication for treatment, in which case haemoglobin < 9.0 g/dL is acceptable. Hepatic function: alanine aminotransferase (ALT) and aspartate aminotransferase (AT) ≤ 2 x upper limit of normal (ULN); Total bilirubin < 1.5x ULN (isolated bilirubin > 1.5x ULN is acceptable if bilirubin is fractioned and direct bilirubin < 35%), except where impaired hepatic function is a consequence of the fast-flow malformation and hence is an indication for treatment, in which case impaired hepatic function is acceptable. Renal function: Serum creatinine < 1.5 x ULN Biochemistry: Calcium (corrected for serum albumin) and magnesium within normal limits or ≤ Grade 1 according to NCI-CTCAE v5.0 if judged clinically not significant by the investigator; Potassium within normal limits or corrected with supplements; Phosphate ≤ 1x ULN. Patient agrees to abstinence or highly effective contraceptive measures if of childbearing potential (WOCBP) Males who are sexually active must use a condom during intercourse while taking mirdametinib and for at least 90 days after stopping mirdametinib and should not father a child in this period. A condom is required to be used also by vasectomised men in order to prevent delivery of the drug via seminal fluid. In addition, male participants must not donate sperm during the study and for at least 90 days after stopping mirdametinib Females who are of child-bearing potential, defined as all individuals physiologically capable of becoming pregnant, must use a highly effective method of contraception during study treatment and for at least 180 days after the last dose of any study treatment. Highly effective contraceptive methods include: Total abstinence (when this is in line with the preferred and usual lifestyle of the subject) Periodic abstinence (eg., calendar, ovulation, symptothermal, post-ovulation methods) and withdrawal are not acceptable methods of contraception; Female sterilisation (have had surgical bilateral oophorectomy with or without hysterectomy), total hysterectomy or bilateral tubal ligation at least 6 weeks before taking study treatment. In case of oophorectomy alone, only when the reproductive status of the women has been confirmed by follow up hormone level assessment; Male partner sterilisation (at least 6 months prior to screening) of the sole partner of a female participant on the study; Use of oral (estrogen and progesterone), injected or implanted combined hormonal method of contraception or placement of an intrauterine device (IUD) or intrauterine system (IUS), or forms of hormonal contraception that have comparable efficacy (failure rate < 1%), for example hormonal vaginal ring or transdermal hormone contraception. In the case of use of oral contraception, women should have been stable on the same pill for a minimum of 3 months before taking study treatment. Women are considered postmenopausal and not of childbearing potential if they have had 12 months of natural (spontaneous) amenorrhoea with an appropriate clinical profile (i.e., age appropriate, history of vasomotor symptoms) or have had surgical bilateral oophorectomy (with or without hysterectomy), total hysterectomy, or bilateral tubal ligation at least 6 weeks before taking study treatment. In the case of oophorectomy alone, only when the reproductive status of the woman has been confirmed by follow up hormone level assessment is she considered to be not of childbearing potential. Patient has signed informed consent and is willing and able to comply with the protocol for the duration of the study, including undergoing treatment and scheduled visits and examinations Exclusion Criteria: History of hypersensitivity to any drugs or metabolites of MEK inhibitors or any of the excipients of mirdametinib Severe infection requiring intravenous antibiotics within 4 weeks prior to enrolment Patient has had a major surgical procedure within 4 weeks prior to enrolment Prior use of a MEK inhibitor Patient has abnormal QT interval corrected by Fridericia's formula (> 450 msec for male participants, > 470 msec for female participants, or > 480 msec for participants with bundle branch block) (triplicate ECG readings taken approximately 2 to 3 minutes apart and averaged) at Screening; Patient is pregnant or lactating at the time of study registration. A pregnancy test is mandated for persons of child-bearing potential in the screening period Impairment of GI function or GI disease that may significantly alter the absorption of the study drug based on investigator discretion Any clinically significant active or known history of liver disease, or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones) Lymphoma, leukaemia, or any malignancy within the past 5 years except for basal cell or squamous epithelial carcinomas of the skin that have been resected with no evidence of metastatic disease for 3 years; Breast cancer within the past 5 years; Known history of Human Immunodeficiency Virus (HIV) infection (testing for HIV is not mandatory in screening) Known history of severe cutaneous reactions like Stevens-Johnson Syndrome (SJS), Toxic Epidermal Necrolysis (TEN), Erythema Multiforme (EM), or Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS) Patient has a history of, or evidence of, retinal pathology on ophthalmologic examination that is considered a risk factor for central serous retinopathy, retinal vein occlusion (RVO), or neovascular macular degeneration. Patients will be excluded from study participation if they have any of the following risk factors for RVO at Screening: Intraocular pressure > 21 mmHg; Serum cholesterol > 7.8 mmol/L; Serum triglycerides > 3.4 mmol/L; Hyperglycaemia (fasting blood glucose > 7.0 mol/L ); Age specific hypertension Patients ≥ 13 years of age with a blood pressure ≥ 140/90 mmHg Patients ≤ 12 years of age with a blood pressure ≥ 95th percentile for age + 12 mmHg Known history of glaucoma Known history of clinically significant, uncontrolled heart disease and/or recent (within 6 months [24 weeks] of signing informed consent/assent) cardiac events including: History of angina pectoris, coronary artery bypass graft (CABG), symptomatic pericarditis, or myocardial infarction within 6 months prior to the start of study treatment; History of documented congestive heart failure (New York Heart Association functional classification III-IV); History of clinically significant cardiac arrhythmias, (e.g., ventricular tachycardia), complete left bundle branch block, high grade Atrioventricular (AV) block (e.g. bifascicular block, Mobitz type II and third degree AV block without pacemaker in place); Uncontrolled hypertension defined by a Systolic Blood Pressure (SBP) ≥ 140 mmHg and/or Diastolic Blood Pressure (DBP) ≥ 90 mmHg, with or without anti-hypertensive medication. Initiation or adjustment of antihypertensive medication(s) is allowed prior to screening; Long QT syndrome, family history of idiopathic sudden death or congenital long QT syndrome, or corrected QT interval > 470 msec at screening (using Fridericia correction); Bradycardia (heart rate < 50 beats per minute at rest), by electrocardiogram (ECG) or pulse Patient has recorded a left ventricular ejection fraction (LVEF) < 55% at Screening Patient has experienced a cerebrovascular accident, transient ischaemic attach, or symptomatic pulmonary embolism within 6 months (24 weeks) of signing informed consent/assent. Patient has other concurrent severe and/or uncontrolled medical conditions that would, in the Treating Physician's judgement, contraindicate administration of mirdametinib (eg. active or uncontrolled severe infection, chronic active hepatitis, immune-compromised, acute or chronic pancreatitis, uncontrolled high blood pressure) Patient is unable to understand and comply with treatment instructions and requirements