⁃ A. Confirmed diagnosis of a malignancy that is high TMB (defined as ≥10 mut/Mb), MSI-high or of proven (previously diagnosed) CMMRD disposition using an analytically validated next-generation sequencing method. Patient cases with TMB between 10-15 mut/Mb may be discussed in an MTB meeting. TMB ≥19 mut/Mb will be fast-tracked for an MTB recommendation, unless there are any patient-specific individualities (such as multiple gene amplifications) that require MTB discussion.

⁃ B. Women of childbearing potential are eligible provide they meet the following criteria:

• 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 with inhibition of ovulation (\[oral, intravaginal or transdermal\]);

⁃ II. progestogen-only hormonal contraception associated with or without inhibition of ovulation (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 atezolizumab, throughout the trial and for five months after the last administration of atezolizumab.

⁃ C. Male patients with partners who are women of childbearing potential are eligible provided that they agree to the following, from the first administration of atezolizumab, throughout the trial until the last administration of atezolizumab:

• Agree to take measures not to father children by using a barrier method of contraception (condom plus spermicide) or sexual abstinence.

• Non-vasectomised male patients with partners who are women of childbearing potential must also be willing to ensure that their partner uses an effective method of contraception.

• Male patients with pregnant or lactating partners must be advised to use barrier method contraception (e.g. condom) to prevent drug exposure of the foetus or neonate.

⁃ All male patients must refrain from donating sperm for the same period.

⁃ D. Patients must be able and willing to undergo a fresh tissue biopsy at baseline and blood samples for translational research. Note that for patients with haematological malignancies or neuroblastomas, blood, bone marrow aspiration and/or trephine or lymph node biopsy samples may be taken.

⁃ E. ADULT PATIENTS (≥18 years): Adequate organ function as per haematological and biochemical indices within the ranges defined in the protocol. These measurements should be performed to confirm the patient's eligibility.

⁃ F. PAEDIATRIC PATIENTS (\<18 years): Adequate organ function as per haematological and biochemical indices within the ranges defined in the protocol. These measurements should be performed to confirm the patient's eligibility.

⁃ G. Patients must have stable thyroid function tests. Patients on stable doses of thyroxine replacement are permitted.