A Study to Evaluate Safety, Tolerability, Dosimetry, and Preliminary Efficacy of the HER2 Directed Radioligand CAM-H2 in Patients With Advanced/Metastatic HER2-Positive Breast, Gastric, and Gastro-Esophageal Junction (GEJ) Cancer

Inclusion Criteria:

1. Informed consent form signed voluntarily before any study-related procedure isperformed, indicating that the patient understands the purpose of, and proceduresrequired for, the study and is willing to participate in the study;

2. Males and females ≥ 18 years of age at screening;

3. Eastern Cooperative Oncology Group performance status (ECOG PS) of 0 to 1;

4. HER2-positive locally advanced or metastatic breast cancer refractory to standardcancer treatment or HER2-positive locally advanced or metastatic gastric or GEJcancer, refractory to standard cancer treatment.

5. Patients should have a minimum of 1 measurable lesion as defined by RECIST version 1.1 or a minimum of 1 measurable lesion as defined by RANO-BM within 4 weeks of thefirst dose of the study drug (Day 1). The lesion has to be a new lesion orprogression of an existing lesion under the current therapy.

6. Any previous anti-HER2 treatment for advanced or metastatic disease is allowed.Patients with breast cancer should have had at least 2 previous systemic anticancertreatments for recurrent, locally advanced or metastatic cancer. Patients withgastric cancer or GEJ cancer should have had at least 1 previous anti-HER2treatment.

7. Life expectancy > 6 months;

8. Adequate organ function, determined by the following laboratory tests:

• Adequate kidney function with an estimated glomerular filtration rate (eGFR) of >59 mL/minute calculated using the Chronic Kidney Disease EpidemiologyCollaboration equation;

• Adequate hepatic function defined as an alanine aminotransferase (ALT) andaspartate aminotransferase (AST) <2.5 x the upper limit of normal (ULN), or <5x ULN in patients with liver metastases, and total bilirubin <2 x ULN;

• Neutrophil count >1500 cells/mm3 without growth factor support (14 days afterlast PEGylated granulocyte colony stimulating factor or 7 days after regulargranulocyte colony stimulating factor);

• Platelet count >100,000 cells/mm3 without platelet transfusion in the last 2weeks;

• Hemoglobin >9.0 g/dL without blood transfusion in the last 2 weeks; and

• Adequate coagulation defined as an international normalized ratio (INR) ≤1.5and activated partial thromboplastin time <1.5 x the upper limit of theinstitutional normal range;

9. Baseline left ventricular ejection fraction ≥ 50% as measured by echocardiography ormultigated acquisition scan.

10. Absence of any psychological, family, sociological, or geographical circumstancethat could potentially represent an obstacle to compliance with the study protocoland the follow-up schedule, as determined by the Investigator. These circumstanceswill be discussed with the patient before enrollment in the study; and

11. Female patients of childbearing potential (ie, ovulating, premenopausal, and notsurgically sterile) must have a negative pregnancy test at screening and prior tostudy drug administration. Patients and their partners of childbearing potentialmust be willing to use 2 methods of contraception, 1 of which must be a barriermethod, for the duration of the study and until 6 months after study drugadministration. Medically acceptable barrier methods include condom with spermicideor diaphragm with spermicide. Medically acceptable non-barrier contraceptive methodsinclude intrauterine devices or hormonal contraceptives (oral, implant, injection,ring, or patch).

Exclusion Criteria:

1. Presence of frank leptomeningeal disease as a unique central nervous system featureor in association with brain parenchymal measurable lesion(s);

2. Symptomatic brain metastases; Note: Patients with asymptomatic treated and untreatedbrain metastases are eligible.

3. Previous local therapy for brain metastases, such as neurosurgery, stereotacticradiotherapy, or whole brain radiotherapy, administered within 6 weeks prior toadministration of CAM-H2; Note: Previous therapy for brain metastases administeredat least 6 weeks prior to CAM-H2 administration will be allowed.

4. For patients with brain metastases, any increase in corticosteroid dose during the 4weeks prior to the first administration of CAM-H2. Note: Corticosteroid treatment in a stable dose or decreasing dose for at least 4weeks prior to the first administration of CAM-H2 is allowed.

5. Uncontrolled intercurrent illness including, but not limited to, ongoing or activeinfection requiring parenteral antibiotics or psychiatric illness/social situationsthat would limit compliance with study requirements;

6. Uncontrolled thyroid disease, defined as free triiodothyronine (T3) and freethyroxine (T4) > 3 x ULN at screening;

7. Uncontrolled diabetes defined as a fasting serum glucose > 2 x ULN or glycatedhemoglobin levels > 8.5% at screening;

8. Gastrointestinal (GI) tract disease resulting in an inability to take oralmedication, malabsorption syndrome, a requirement for intravenous (IV) alimentation,prior surgical procedures affecting absorption, or uncontrolled inflammatory GIdisease (eg, Crohn's, ulcerative colitis);

9. Current active hepatic or biliary disease (exception of patients with Gilbert'ssyndrome, asymptomatic gallstones, liver metastases, or stable chronic liver diseaseper Investigator assessment);

10. Ongoing peripheral neuropathy of Grade > 2 according to the Common TerminologyCriteria for Adverse Events (CTCAE) version 5.0;

11. Severe and/or uncontrolled medical conditions or other conditions that could affectparticipation in the study such as:

• Symptomatic congestive heart failure of New York Heart Association Class III orIV;

• Unstable angina pectoris, symptomatic congestive heart failure, myocardialinfarction within 6 months of start of study drug, serious uncontrolled cardiacarrhythmia, or any other clinically significant cardiac disease; or

• Liver disease, including cirrhosis and severe hepatic impairment;

12. Active (acute or chronic) or uncontrolled severe infections;

13. Known history of HIV, hepatitis B, or active hepatitis C virus at screening;

14. Prior investigational anticancer therapy within 4 weeks prior to the firstadministration of CAM-H2.

15. Patients who have had a major surgery or significant traumatic injury within 4 weeksprior to the first administration of CAM-H2, who have not recovered from sideeffects of any major surgery (defined as requiring general anesthesia), or have amajor surgery planned during the course of the study;

16. Other malignancies within the past 3 years except for adequately treated carcinomaof the cervix or basal or squamous cell carcinomas of the skin or stage I uterinecancer;

17. Radiation therapy for metastatic disease foci outside the brain, administered within 3 weeks prior to the first administration of CAM-H2;

18. Known hypersensitivity to any of the study drugs (including inactive ingredients),including iodine allergy;

19. History of significant comorbidities that, in the Investigator's judgement, mayinterfere with study conduct, response assessment, or informed consent;

20. Unable or unwilling to complete the study procedures;

21. Patients that cannot be hospitalized in a radionuclide therapy room;

22. Patients with urinary incontinence;

23. Patients that are unable to comply with thyroid protective pre-medication;

24. Patients in whom bladder catheterization cannot be performed, or in patients who areunwilling to be catheterized if necessary;

25. Patients with contraindications for undergoing MRI or computed tomography (CT),including for receiving contrast agents; or

26. Patient is the Investigator or sub-Investigator, research assistant, pharmacist,study coordinator, or other staff or relative thereof, who is directly involved inthe conduct of the study.