Inclusion Criteria:
1. Participants with advanced solid tumors (locally advanced, unresectable or metastatic head and neck
squamous carcinoma, metastatic gastric carcinoma, metastatic colorectal cancer or any other metastatic
tumor, for example NSCLC, breast cancer, pancreatic cancer, and melanoma) confirmed by histology or
cytology.
2. Presence of cancer lesion(s) (target or non-target lesions per RECIST 1.1) on standard of care images.
3. Male or non-pregnant, non-lactating female age ≥18 years.
Female participants of child-bearing potential and male participants (if sexually active) must agree to use
adequate method(s) of effective contraception during their participation in the study.
a. Medically acceptable adequate contraception for sexually active females with child-bearing
potential include: 1) surgical sterilization (such as tubal ligation or hysterectomy), 2) approved
hormonal contraceptives, 3) barrier method (such as condom or diaphragm) used with a
spermicide, or 4) intrauterine device (IUD).
b. Medically acceptable adequate contraception for sexually active males include: 1) surgical
sterilization (such as vasectomy), 2) a condom used with a spermicide.
4. Eastern Cooperative Oncology Group (ECOG) Performance Status ≤2.
5. Adequate hepatic function as defined below (within 28 days of dosing with 68Ga-R12961):
a. Serum alanine aminotransaminase (ALT)/ aspartate aminotransaminase (AST) ≤3 × upper limit
of normal (ULN) or ≤5 × ULN if liver metastases are present, and
b. Serum bilirubin: total ≤1.5 × ULN (unless due to Gilbert’s syndrome or hemolysis in which
case total ≤3.0 × ULN).
Adequate renal function as measured by creatinine clearance calculated by the Cockcroft-Gault formula
(≥45 mL/minute), determined within 28 days of dosing with 68Ga-R12961.
7. Able to understand and willing to sign an informed consent form.

Exclusion Criteria:
1. Received any clinical study drug or treatment targeting CCR8, CC chemokine receptor type 4 (CCR4) or
anti-cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) in the 2 months preceding the planned
68Ga-R12961 imaging date.
2. Radiotherapy ≤14 days prior to dosing with 68Ga-R12961.
3. Received a radionuclide within a period of less than 10 physical half-lives of the administered
radionuclide prior to dosing with 68Ga-R12961.
4. Major surgery ≤21 days prior to dosing with 68Ga-R12961 or has not recovered from adverse effects of a
prior surgery.
5. Severe or unstable medical condition, such as congestive heart failure (New York Heart Association
[NYHA] Class III or IV), ischemic heart disease, uncontrolled hypertension, uncontrolled diabetes
mellitus, as well as an uncontrolled cardiac arrhythmia requiring medication (≥Grade 2, according to
NCI-CTCAE, Version 5.0), myocardial infarction within 6 months prior to starting Investigational
Product, or any other significant or unstable concurrent cardiac illness. Note: Stable chronic atrial
fibrillation is allowed.
6. History of cerebrovascular accident within 6 months or that resulted in ongoing neurologic instability.
7. Major active infections requiring treatment.
8. Any acute illness including COVID and influenza A/B within 14 days prior to dosing with 68Ga-R12961
unless mild in severity, as assessed by the Investigator.
9. Congenital long QT syndrome or corrected QT interval by Fridericia (QTcF) interval ≥470 msec.
10. Any other condition that in the opinion of the Investigator would place the participant at an unacceptable
risk or cause the participant to be unlikely to fully participate or comply with study procedures.
11. Certain drugs (Appendix 3) that are known to lead to drug interaction by significant inhibition of major
transporters, should not be administered on the day of 68Ga-R12961 administration in the Dosimetry
Phase.