Goal of the observational study: Based on PET/MRI data it is possible to differentiate between complete and incomplete pathological remission after neoadjuvant systemic therapy in HER2-positive breast cancer patients.

The main question it aims to answer are:

Primary endpoint:

1) Sensitivity and specificity as co-primary endpoints for identification of HER2-positive breast carcinoma with complete pathologic remission (pCR; yT0 yN0) using 18F-FDG PET/MRI (response assessment)

Secondary endpoint(s):

1. Accuracy for the identification of patients with HER2-positive breast carcinoma with complete pathologic remission (pCR; yT0 yN0) using 18F-FDG PET/MRI (response assessment)
2. Sensitivity, specificity, and accuracy for the identification of patients with HER2-positive breast carcinoma with complete pathologic remission (pCR) of the primary (yT0) after neoadjuvant therapy using 18F-FDG PET/MRI (response assessment)
3. Sensitivity, specificity, and accuracy for the identification of patients with HER2-positive breast carcinoma with complete pathologic remission (pCR) of locoregional lymph node metastases (yN0) after neoadjuvant therapy using 18F-FDG PET/MRI (response assessment)
4. Evaluation of pre-treatment (baseline) 18F-FDG PET/MRI for predicting therapy response of the primary and locoregional lymph node metastases in patients with HER2-positive breast carcinoma supported by artificial-intelligence (prediction)
5. Evaluation of 18F-FDG PET/MRI for predicting therapy response of the primary in patients with HER2-positive breast carcinoma after the first cycles of systemic therapy supported by artificial-intelligence (prediction)
6. Evaluation of 18F-FDG PET/MRI for predicting therapy response of locoregional lymph node metastases in patients with HER2-positive breast carcinoma after the first cycles of system therapy supported by artificial-intelligence (prediction)

The guideline-recommended staging procedure (S3 Germany) using CT will be replaced by a whole-body 18F-FDG PET/MRI, including dedicated 18F-FDG PET/MRI of the breast. The histopathologic results of tissue samples obtained during routine clinical treatment after successful neoadjuvant systemic therapy will serve as a reference standard.

The study protocol involves the following examinations for all included patients:

1. Baseline (pre-treatment) examination to substitute for the staging examinations specified in the S3 guideline: Initial whole-body 18F-FDG PET/MRI including 18F-FDG PET/MRI of the breast
2. Thoracic 18F-FDG PET/MRI including 18F-FDG PET/MRI of the breast after the first two cycles of systemic therapy
3. Thoracic 18F-FDG PET/MRI including 18F-FDG PET/MRI of the breast after completion of systemic therapy and immediately before clinically indicated surgery

Inclusion Criteria:

• Female
• HER2-positive breast carcinoma
• legally competent female patients aged ≥ 18 years
• willing and able to attend scheduled examinations
• written informed consent for study participation
• decision to receive neoadjuvant systemic therapy / exclusion of distant metastases

Exclusion Criteria:

• previous cancer diagnosis within the last five years or second, synchronous malignancy
• contraindication to MRI examination
• severe renal insufficiency
• pregnancy or lactation

In this study, we aim to enrol biological women with newly diagnosed HER2-positive breast carcinoma.

In this study, we aim to enrol women with newly diagnosed HER2-positive breast carcinoma. For details please see Inclusion/Exclusion criteria.