Inclusion Criteria:

- Patients (all genders) must be >= 18 years of age.

- Patient must have the ability to understand and the willingness to sign a written
informed consent document. Patients with impaired decision-making capacity (IDMC) who
have a legally authorized representative (LAR) or caregiver and/or family member
available will also be considered eligible.

- Patient must have an Eastern Cooperative Oncology Group (ECOG) performance status of
0-2.

- Patient must have histologically confirmed HER2-positive primary invasive breast
carcinoma by American Society of Clinical Oncology (ASCO)/College of American
Pathologists (CAP) guidelines that has been determined by local testing.

- Patient must have known (either positive or negative) hormone receptor (estrogen
receptor [ER] or progesterone receptor [PR]) status by local testing, per ASCO/CAP
guidelines. Patients with either hormone receptor-positive or hormone receptor-
negative HER2-positive breast cancer are eligible.

- Patient must have American Joint Committee on Cancer (AJCC) 8th Edition stage IIa-IIIc
according to anatomic staging table at diagnosis and below criteria.

- Patients without nodal involvement (cN0) are eligible if T size > 2.0 cm (T2-4)

- Patients with nodal involvement (cN1-3) are eligible if T2-4

- Patients with clinical T4d are not eligible

- Patients with bilateral invasive breast cancers are eligible if both cancers are
HER2-positive and at least one meets all protocol eligibility criteria and neither
cancer renders the patient ineligible.

- Patients with multiple ipsilateral invasive tumors are eligible as long as all tumors
are HER2-positive and at least one tumor focus meets all eligibility criteria.
Multiple lesions that appear part of the same index tumor do not require additional
biopsy/HER2 testing.

- Patient must plan to start a standard neoadjuvant pertuzumab (or other biosimilars)
based regimen.

- Patients with a prior or concurrent malignancy whose natural history or treatment does
not have the potential to interfere with the safety or efficacy assessment of this
imaging intervention are eligible for this trial.

- Patients with human immunodeficiency virus (HIV) on effective anti-retroviral therapy
with undetectable viral load within 6 months of registration are eligible for this
trial.

- Patient must be participating in the trial at an institution which has agreed to
perform the imaging research studies, completed the Eastern Cooperative Oncology
Group-American College of Radiology Imaging Network Cancer Center Group (ECOG-ACRIN)
defined PET/CT scanner qualification procedures and received ECOG-ACRIN PET/CT scanner
approval.

- For patients who completed the baseline (T0) FDG-PET/CT PRIOR to registration,
neoadjuvant pertuzumab-based regimen must start after study registration and
within 21 days after the T0 scan.

- Patients must not have used colony stimulating growth factors within 14 days
prior to completing a T0 scan done prior to registration.

Exclusion Criteria:

- Patient must not have any prior treatment for the current breast cancer, including
surgery, chemotherapy, hormonal therapy, radiation or experimental therapy.

- Patient must not be pregnant or breast-feeding due to the potential harm to an unborn
fetus and possible risk for adverse events in nursing infants with the teratogenic
effects of FDG in addition to the radiation exposure during PET/CT. All patients of
childbearing potential must have a blood test or urine study within 7 days prior to
registration to rule out pregnancy.

- NOTE: A pregnancy test within 7 days prior to the T0 scan is also required but
will only need to be done if a) the T0 scan is completed after study registration
and b) if the pregnancy test done prior to registration is completed outside of
the 7-day window.

A patient of childbearing potential is defined as anyone, regardless of sexual orientation
or whether they have undergone tubal ligation, who meets the following criteria: 1) has
achieved menarche at some point, 2) has not undergone a hysterectomy or bilateral
oophorectomy; or 3) has not been naturally postmenopausal (amenorrhea following cancer
therapy does not rule out childbearing potential) for at least 24 consecutive months (i.e.,
has had menses at any time in the preceding 24 consecutive months).

- Patient must not have any contraindication to FDG-PET/CT imaging which includes
routine glucose values > 200 mg/dL and severe claustrophobia.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.

Eligibility last updated 7/24/23. Questions regarding updates should be directed to the study team contact.