The structure of the functional reserve in various breast cancer treatment regimens as a rationale for differentiated rehabilitation: a retrospective cohort study

BACKGROUND: Antitumor treatment regimens determine a specific profile of impairments in the body’s ability to tolerate antitumor therapy and physical activity without clinically significant decompensation, which is defined in this study as functional reserve. Existing medical rehabilitation programs for breast cancer have been developed without considering the underlying mechanism of impairment, and the use of a single protocol in a clinically heterogeneous population is not methodologically justified. AIM: To study the frequency and structure of cardiorespiratory, neuromuscular, and nutritional impairments of functional reserve in patients with breast cancer depending on the antitumor treatment regimen and to substantiate the need for a differentiated approach to medical rehabilitation. METHODS: A retrospective cohort study was conducted based on data from the electronic medical system of the Ivanovo Regional Oncology Dispensary for 2023–2025. All patients (n=890) had verified breast cancer and received treatment according to current clinical guidelines. Patients were divided into four groups: Group 1—surgery ± sentinel lymph node biopsy ± radiation therapy ± hormonal therapy (n=234); Group 2—surgery with axillary lymph node dissection ± radiation therapy ± hormonal therapy (n=203); Group 3—anthracycline-containing chemotherapy ± taxanes/platinum agents ± anti-HER2 therapy ± radiation therapy (n=354); Group 4—systemic therapy for metastatic breast cancer: CDK4/6 inhibitors ± hormonal therapy ± palliative chemotherapy ± anti-HER2 therapy for stage IV disease (n=99). Cardiorespiratory, neuromuscular, and nutritional outcomes were assessed. The χ² test with pairwise comparisons and Bonferroni correction was used to compare categorical variables between groups, and the Kruskal–Wallis test was used for quantitative variables. RESULTS: At least one impairment of functional reserve was identified in 571 patients (64.2%). The disorder profiles differed significantly between the groups (p 0.001). In Group 2, lymphedema was the predominant complication (65.0%); in Group 3, cardiotoxicity (35.3%), neuropathy (15.3%); and in Group 4, nutritional depletion (19.2%), dyspepsia (37.4%), and mortality during follow-up (62.6%). Chemotherapy dose reductions were recorded in 15.8% of patients in Group 3 and 14.1% in Group 4. Based on the identified disorder profiles, a core set of disability domains in International Classification of Functioning, Disability and Health categories was developed for each group. CONCLUSION: The anticancer treatment regimen defines a specific profile of functional reserve impairments, precluding the possibility of a single rehabilitation protocol for breast cancer. Systematization of impairments within International Classification of Functioning, Disability and Health categories creates a structured basis for planning differentiated rehabilitation programs. The data obtained determines the direction of functional reserve, while the rehabilitation diagnosis remains individualized for each patient. The retrospective design and registry-based data source limits the completeness of impairment identification due to the lack of standardized rehabilitation tools; the single-center nature of the study limits the external validity of the results.