Inclusion Criteria:
1. Pathologically confirmed estrogen and/or progesterone receptor (ER/PR) positive and human epidermal
growth factor 2 (HER2) negative (IHC 0, 1+ or 2+/ in situ hybridization (ISH) not-amplified) locoregionally
recurrent or metastatic breast cancer. ER/PR positivity must be defined by the 2020 American Society of
Oncology (ASCO)/College of American Pathologist (CAP) guidelines, respectively (Allison et al. 2020).
2. Refractory to endocrine therapy (progression on at least one line of endocrine therapy and determined by the
investigator that the Study Participant would not benefit from additional endocrine therapy). Note: there is no
limit on prior number of lines of endocrine therapy or prior treatments with CDK4/6, AKT, PI3K and/or
mTOR inhibitors.
3. Received at least one line of chemotherapy or antibody drug conjugate in the locoregionally recurrent or
metastatic setting.
4. At least one measurable target lesion per RECIST v1.1 criteria within 28 days prior to dosing with 68Ga-
R11228.
5. Male or non-pregnant, non-lactating female subjects age ≥18 years.
6. Study Participants of childbearing potential and male Study Participants must agree to adequate contraception
during the screening and treatment period and until 6 months after last study treatment. Medically acceptable adequate contraception for sexually active females in non-same sex relationships with childbearing potential
include: 1) surgical sterilization (such as tubal ligation or hysterectomy), 2) surgically sterilized partner 3)
approved hormonal contraceptives, 4) barrier method (such as condom or diaphragm) used with a spermicide,
or 5) intrauterine device (IUD). Medically acceptable adequate contraception for sexually active males in non-
same sex relationships include: 1) surgical sterilization (such as vasectomy), 2) a condom used with a
spermicide.
7. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1.
8. Life expectancy of at least six months.
9. Adequate bone marrow reserve as evidenced by:
o Absolute neutrophil count ≥1,500/μl
o Absolute lymphocyte count ≥1,000/μl
o Platelet count ≥100,000/μl
o Hemoglobin ≥9 g/dL (without need for hematopoietic growth factor or transfusion support)
10. Adequate hepatic function as defined below:
o Serum alkaline phosphatase ≤3 × upper limit of normal (ULN) unless bone metastases, in which case
liver specific alkaline phosphatase must be separated from the total and use to assess liver function,
and
o Serum alanine aminotransaminase (ALT)/ aspartate aminotransaminase (AST) ≤3 × upper limit of
normal (ULN) or ≤5 × ULN if liver metastases are present, and
o Serum total bilirubin ≤1.5 × ULN (unless due to Gilbert’s syndrome in which case total ≤3.0 ×
ULN).
11. Adequate renal function as demonstrated by creatinine clearance calculated by the Cockcroft-Gault formula to
be equal or higher than 60 mL/minute.
12. Able to understand and willing to sign a written informed consent form.

Exclusion Criteria:
1. Study participant has not recovered from clinically significant adverse event(s) resulting from most recent 177Lu-R11228/68Ga-R11228
Clinical Study Protocol Phase 1: R11228-101 Page 8 of 107
Confidential Radionetics Oncology, Inc.
adequate contraception for sexually active females in non-same sex relationships with childbearing potential
include: 1) surgical sterilization (such as tubal ligation or hysterectomy), 2) surgically sterilized partner 3)
approved hormonal contraceptives, 4) barrier method (such as condom or diaphragm) used with a spermicide,
or 5) intrauterine device (IUD). Medically acceptable adequate contraception for sexually active males in non-
same sex relationships include: 1) surgical sterilization (such as vasectomy), 2) a condom used with a
spermicide.
7. Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1.
8. Life expectancy of at least six months.
9. Adequate bone marrow reserve as evidenced by:
o Absolute neutrophil count ≥1,500/μl
o Absolute lymphocyte count ≥1,000/μl
o Platelet count ≥100,000/μl
o Hemoglobin ≥9 g/dL (without need for hematopoietic growth factor or transfusion support)
10. Adequate hepatic function as defined below:
o Serum alkaline phosphatase ≤3 × upper limit of normal (ULN) unless bone metastases, in which case
liver specific alkaline phosphatase must be separated from the total and use to assess liver function,
and
o Serum alanine aminotransaminase (ALT)/ aspartate aminotransaminase (AST) ≤3 × upper limit of
normal (ULN) or ≤5 × ULN if liver metastases are present, and
o Serum total bilirubin ≤1.5 × ULN (unless due to Gilbert’s syndrome in which case total ≤3.0 ×
ULN).
11. Adequate renal function as demonstrated by creatinine clearance calculated by the Cockcroft-Gault formula to
be equal or higher than 60 mL/minute.
12. Able to understand and willing to sign a written informed consent form.
Exclusion Criteria:
1. Study participant has not recovered from clinically significant adverse event(s) resulting from most recent
anticancer therapy/intervention prior to Day 1 of 68Ga-R11228 injection.
2. Known central nervous system (CNS) disease, except for those subjects with treated brain metastasis who are
stable for at least 1 month, having no evidence of progression or hemorrhage after treatment and no ongoing
requirement for corticosteroids, as ascertained by clinical examination and brain imaging (magnetic resonance
imaging [MRI] or computed tomography [CT]) during the screening period.
3. Radiotherapy for breast cancer ≤ 28 days prior to study Day 1.
4. Received a radionuclide within a period of less than 10 physical half-lives of the administered radionuclide
prior to dosing with 68Ga-R11228.
5. Major surgery ≤ 21 days prior to study Day 1 or has not recovered from adverse effects of such procedure.
6. Severe or unstable medical condition, such as congestive heart failure (New York Heart Association [NYHA]
Class III or IV), ischemic heart disease, uncontrolled hypertension (average systolic blood pressure ≥140
mmHg or an average diastolic blood pressure ≥90 mmHg, based on medical records), 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 study drug, or any other
significant or unstable concurrent cardiac illness. Note: Stable chronic atrial fibrillation is allowed.
7. Congenital long QT syndrome or corrected QT interval by Fridericia (QTcF) interval ≥470 msec.
8. History of other previous or concurrent cancer that would interfere with the determination of safety.
9. Major active infection requiring antibiotics.
10. Acute illness ≤ 14 days prior to study Day 1, unless mild in severity, as assessed by the Investigator.
11. Any other condition that in the opinion of the Investigator would place the subject at an unacceptable risk or
cause the subject to be unlikely to fully participate or comply with study procedures.