Supervised Exercise to Promote Infiltration of NK-cells Into the Tumor

Inclusion Criteria: * stage I-III breast cancer * scheduled for neoadjuvant chemotherapy with 2 or 3-weekly Adriamycin/Cyclofosfamide, followed by Paclitaxel weekly +/- trastuzumab * willing to undergo an additional ultrasound guided biopsy * ECOG-performance score ≤ 2 (able to perform basic activities of daily living such as walking or biking) Exclusion Criteria: * addition of immuno- or targeted therapy at start of neoadjuvant chemotherapy * currently participating in structured vigorous aerobic exercise and/or resistance exercise (≥2 days per week). * cognitive disorder or severe emotional instability * presence of other disabling co-morbidity that might hamper physical exercise e.g. heart failure (NYHA classes 3 and 4), chronic obstructive pulmonary disease (COPD, gold 3 and 4), orthopaedic conditions and neurological disorders (e.g., hernia, paresis, amputation, active rheumatoid arthritis); * immunosuppressive medication (e.g. corticosteroids (other than used as part of standard chemotherapy premedication protocol), cyclosporine) * immunodeficiency (primary or secondary) * impossibility to perform an ultrasound-guided biopsy of the tumor