2.0 - Amendment issued before first subject visit.

3.0 - Internal version only

4.0 - Amendment issued before first subject visit

5.0 - Updated trial objectives to evaluate ORR at 6 months instead of up to 3 years and evaluate CNS/LM progression instead of CNS progression free survival. Also deleted objective comparing the OS to historical controls. Added instruction on dosing potassium iodine and referred to FDA and European Association of Nuclear Medicine guidelines on potassium iodide dosing in the “treatment” section to ensure subject safety Added clarification for difference between treatment before and after interim analysis throughout protocol Added to safety considerations section a minimum of one week is an adequate time period between support for myelosuppresion and IMP administration Changed follow-up to include SAEs considered related to 131Iomburtamab or new onset of cancers regardless of causality Changed inclusion criteria - Clarified life expectancy as judged by investigator - Deleted time period between hematological support and 131Iomburtamab administration (referred to in protocol text instead) - Narrowed liver function criteria to appropriate levels and exclude subjects with Hy’s law criteria at screening Changed exclusion criteria to permit CSF flow study be made with several different 111Indium. Updated secondary endpoints to reflect changes made in the objectives. Added text on location and characterization of metastatic lesions to “medical and surgical history” section so that important medical history information are specified and collected

6.0 - internal version only

7.0 -Change of no. of non-MSK patients in the interim analysis - Specify removal of dosimetry doses after completion of the interim analysis - Specify when informed consent must be obtained In case the indwelling intracerebroventricular access device (e.g., Ommaya) is placed in connection with the tumor resection - Updated text on thyroid protection - Dose of dexamethasone changed - Text added for clarification re. patient treatment discontinuation - Addition of chemical meningitis to pre-defined AEs of special interest

8.0 - internal version

9.0 - 3 new assessments were added to distinguish between CNS/LM progression and systemic progression A new secondary objective was added: To evaluate CNS/LM progression-free survival (CNS/LM PFS) at 12 months (primary interim objective) Text and sections have been deleted for treatment and procedures required before the interim analysis until 31 December 2019 to reflect that dosimetry is not part of the protocol after 01 January 2020.

10.0 -Addition of two efficacy objectives - To evaluate CNS/LM progression-free survival (CNS/LM PFS) at 6 months - To evaluate Overall Survival (OS) at 12 months The following endpoints were added to address the above efficacy objectives: - CNS/LM PFS at 6 months will be estimated based on time from first treatment dose to CNS/LM progression or death from any cause. Subjects alive without CNS/LM progression at time of analysis will be censored at last date of disease evaluation without evidence of progression. - OS at 12 months will be estimated – based on the time from first treatment dose to death by any cause. Subjects alive at time of analysis, are censored at last date known to be alive Furthermore, the objective “To evaluate CNS/LM progression-free survival (CNS/LM PFS) at 12 months” was changed from an interim objective to an overall objective.