DETERMINE Trial Treatment Arm 04: Trastuzumab in Combination With Pertuzumab in Adult, Teenage/Young Adult and Paediatric Patients With Cancers With HER2 Amplification or Activating Mutations

THE PARTICIPANT MUST FULFIL THE ELIGIBILITY CRITERIA WITHIN THE DETERMINE MASTER PROTOCOL (NCT05722886) AND WITHIN THE TREATMENT ARM 04 (TRASTUZUMAB AND PERTUZUMAB) OUTLINED BELOW*

*When trastuzumab and pertuzumab-specific inclusion/exclusion criteria or precautions belowdiffer from those specified in the Master Protocol, the trastuzumab and pertuzumab -specific criteria will take precedence. Inclusion Criteria:

A. Confirmed diagnosis of a malignancy harbouring HER2 amplification, or an appropriateactivating mutation as defined by the MTB, using an analytically validated method.

B. Age 12 years or above. C. Women of childbearing potential are eligible provided that they meet the followingcriteria: Have a negative serum or urine pregnancy test before enrolment and; Agree to use one form of effective birth control method such as: I. combined (oestrogen and progestogen containing) hormonal contraception associated withinhibition of ovulation (oral, intravaginal or transdermal): II. progestogen-only hormonal contraception associated with or without inhibition ofovulation (oral, injectable or implantable) III. intrauterine device (IUD) IV. intrauterine hormone-releasing system (IUS) V. bilateral tubal occlusion VI. vasectomised partner VII. sexual abstinence VIII. male or female condom with or without spermicide IX. cap, diaphragm or sponge with spermicide Effective from the first administration of trastuzumab or pertuzumab (whichever is first),throughout the trial and for seven months after the last administration of trastuzumab orpertuzumab (whichever is later). D. Male patients with partners who are women of childbearing potential are eligibleprovided that they agree to the following, from the first administration of trastuzumab orpertuzumab (whichever is first), throughout the trial and for seven months after the lastadministration of trastuzumab or pertuzumab (whichever is later):

• Agree to take measures not to father children by using a barrier method ofcontraception or to sexual abstinence.
• Non-vasectomised male patients with partners who are women of childbearing potentialmust also be willing to ensure that their partner uses an effective method ofcontraception as in C, above.
• Male patients with pregnant or lactating partners must be advised to use barriermethod contraception (e.g. condom) to prevent drug exposure of the foetus or neonate.

E. Patients must be able and willing to undergo a fresh biopsy.

F. ADULT PATIENTS: Adequate organ function as per haematological and biochemical indiceswithin the ranges shown below. These measurements should be performed to confirm thepatient's eligibility. Haemoglobin (Hb): ≥90 g/L (transfusion allowed) Absolute neutrophil count (ANC): ≥1.5x10^9g/L (no GCSF support in preceding 72 hours) Platelet count: ≥100x10^9g/L (unsupported for 72 hrs) Bilirubin: <1.5 × upper limit of normal (ULN) Patients with known Gilbert disease: totalbilirubin ≤3 × ULN Alanine aminotransferase (ALT) and aspartate aminotransferase (AST): ≤2.5 × ULN or ≤5 × ULNif raised due to metastases Estimated glomerular filtration rate (eGFR): >30 mL/min Coagulation - prothrombin (PT) (or international normalized ratio [INR]) and activatedpartial thromboplastin clotting time (aPTT): <1.5 × ULN (unless patient is onanticoagulants, e.g. warfarin [INR should be stable and within indicated therapeuticrange], or direct oral anticoagulants [DOAC])

G. PAEDIATRIC PATIENTS aged 12-15 years: Adequate organ function as per haematological andbiochemical indices within the ranges shown below. These measurements should be performedto confirm the patient's eligibility. Haemoglobin (Hb): >80 g/L (transfusion allowed) Absolute neutrophil count (ANC): >0.75×10^9/L (no GCSF support in preceding 72 hours) Platelet count: ≥75×10^9/L (unsupported for 72 hrs) Bilirubin: ≤1.5 × ULN for age Alanine aminotransferase (ALT) and aspartate aminotransferase (AST): ≤2.5 × ULN or ≤5 × ULNif raised due to metastases Estimated glomerular filtration rate (eGFR): ≥60 mL/min (uncorrected value) Coagulation - prothrombin (PT) (or international normalized ratio [INR]) and activatedpartial thromboplastin clotting time (aPTT): ≤1.5 × ULN for age (unless patient is onanticoagulants, e.g. warfarin [INR should be stable and within indicated therapeuticrange], or DOAC.

Exclusion Criteria:

A. Diagnosis of HER2-positive early or metastatic breast cancer.

B. Patients with rapidly progressing or symptomatically deteriorating brain metastases.Patients with previously treated brain metastases are eligible, provided the patient hasnot experienced a seizure or had a clinically significant change in neurological statuswithin the 14 days prior to the start of IMP administration. Such patients must benondependent on steroids or on a stable or reducing dose of steroid treatment for at least 14 days (or 7 days for paediatric patients) prior to the start of IMP administration.Primary brain or central nervous system (CNS) malignancies are allowed providing thepatient is clinically stable (if requiring corticosteroids must be at stable or decreasingdoses for at least 14 days for adults and 7 days for paediatric patients prior to the startof IMP administration). Patients who have received brain irradiation must have completedwhole-brain radiotherapy and/or stereotactic radiosurgery at least 14 days prior to thestart of IMP administration. C. Female patients who are pregnant, breastfeeding or planning to become pregnant duringthe trial or within seven months following their last dose of trastuzumab or pertuzumab (whichever is later). D. Severe dyspnoea at rest due to complications of advanced malignancy or requiringsupplementary oxygen therapy.

E. Known hypersensitivity to trastuzumab or pertuzumab, murine proteins, or to any of theexcipients.

F. Patients with clinically significant pre-existing cardiac conditions, includinguncontrolled or symptomatic angina, uncontrolled atrial or ventricular arrhythmias (within 6 months), NYHA class III or IV congestive heart failure. Patients with a cerebrovascularevent (including stroke or transient ischaemic attack [TIA]) or cardiovascular event (including acute myocardial infarction [MI]) within six months before the first dose oftrastuzumab and pertuzumab. Left Ventricular Ejection Fraction <55%.

G. Prior treatment with the same class of drug unless genetic profile demonstrates amechanism of resistance known to be potentially sensitive to trastuzumab or pertuzumab.

H. Any clinically significant concomitant disease or condition (or its treatment) thatcould interfere with the conduct of the trial or absorption of oral medications or thatwould, in the opinion of the Investigator, pose an unacceptable risk to the patient in thistrial.