Cancer has emerged as a prominent cause of mortality in the 21st century, with breast cancer (BC) being the most diagnosed malignancy. Multidisciplinary cancer management has improved survival chances, but side effects and long-term consequences of treatments have significant implications for cancer survivors' health-related quality of life. Exercise is increasingly considered and used in cancer treatment and follow-up. However, studies demonstrating the biological mechanisms underlying the anticarcinogenic effects (ACE) of exercise are insufficient to justify the most appropriate physical activity for different clinical scenarios. Achieving scientific excellence in understanding the ACE of exercise in cancer management is critical to optimize treatment and enhance patients' quality of life.

Inclusion Criteria (intervention group):

• Reproductive age (premenopausal);
• Diagnosis of Stage II-III Triple-Negative Breast Cancer (TNBC) (negative for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2));
• Timeframe of 3 to 9 months after completion of surgery, adjuvant chemotherapy, radiation therapy, and/or immunotherapy;
• Physician-certified (cardiologist) physical fitness for exercise testing, supported by echocardiography (ECHO).

Inclusion Criteria (control group):

• Reproductive age (premenopausal);
• No current or prior diagnosis of any type of cancer;
• Matched by age, body constitution, and physical fitness to the breast cancer participant group.

Exclusion Criteria:

• Pregnancy;
• Autoimmune diseases (e.g., thyroiditis, inflammatory bowel disease, atopic dermatitis, etc.);
• Endocrine disorders (e.g., metabolic syndrome, diabetes);
• Cardiovascular diseases;
• Diagnosis of any other type of oncological disease;
• Any condition for which physical activity is contraindicated (e.g., asthma, COPD, spinal disc herniation, severe iron deficiency anemia).

Individual participant data (IPD) will be available beginning 6 months after the publication of the final study results. The data will remain accessible for a period of 5 years following the initial release.

De-identified individual participant data that underlie the results reported in this study will be shared with researchers and interested parties who provide a methodologically sound proposal via RSU dataverse. To gain access, data requestors must submit a formal request to the Principal Investigator (Dace Reihmane, dace.reihmane@rsu.lv) and sign a data access agreement. Requests will be reviewed by the study team and Riga Stradiņš University (RSU) Data Security and Management Unit to ensure compliance with GDPR and FAIR principles.