Supervised Exercise During Neoadjuvant Chemotherapy for Breast Cancer

Inclusion Criteria:

1. Histologically confirmed invasive breast carcinoma, clinical stage I-III.
2. Female, age ≥18 years.
3. Planned to undergo standard neoadjuvant chemotherapy of ≥4 months duration with curative intent, followed by definitive surgery. This includes common regimens such as taxane- and anthracycline-based chemotherapy or TCHP (docetaxel, carboplatin, trastuzumab, pertuzumab) for HER2-positive disease.
4. Availability of a baseline CT or PET/CT scan (as part of routine diagnosis or staging) that includes axial images at the third lumbar vertebra (L3) level, performed prior to starting NACT.
5. Anticipated post-NACT CT or PET/CT scan (e.g. for re-staging) that includes the L3 level, to be performed after completion of NACT and before surgery per standard care practice.
6. Eastern Cooperative Oncology Group (ECOG) performance status 0-2.
7. Cleared by treating oncologist and physiotherapist as medically able to participate in a moderate-intensity exercise program (e.g. able to walk independently with or without an assistive device and perform basic resistance exercises).
8. Able and willing to provide written informed consent.
9. Able to understand study instructions and complete questionnaires.

Exclusion Criteria:

1. Evidence of distant metastatic disease (stage IV) or treatment plan not aiming for curative intent.
2. Unstable or severe cardiac, pulmonary, or other systemic comorbidities that would make moderate exercise unsafe, such as unstable angina or recent myocardial infarction, decompensated heart failure, uncontrolled severe arrhythmia, uncontrolled severe hypertension, or severe symptomatic lung disease.
3. Major musculoskeletal or neurological conditions that would preclude safe participation in supervised exercise (e.g. unstable orthopedic injuries, severe neuropathy or neurologic deficit, or recent major surgery not yet recovered).
4. Current second active malignancy (excluding second localized early breast cancer).
5. Regular participation in ≥150 minutes per week of moderate-vigorous aerobic activity and ≥2 resistance training sessions per week in the 3 months before cancer diagnosis.
6. Baseline imaging not available or not including L3, or patient unlikely to have a post-NACT scan including L3 (e.g. if they refuse imaging).
7. CT images of insufficient quality (e.g. severe artifacts or truncated field of view at L3) that would prevent accurate muscle measurement.
8. Pregnant or breastfeeding at the time of enrollment.
9. Significant cognitive impairment, psychiatric disorder, or language barrier that would prevent informed consent or compliance with the protocol.
10. Any other condition or circumstance that, in the opinion of the investigator, would make participation not in the patient's best interest or would compromise the scientific integrity of the study.