Associations of Breast Cancer Treatments with One-Year Changes in Health-Related Fitness

<b>Background/Objectives:</b> Early-stage breast cancer treatments adversely affect components of health-related fitness (HRF) important for treatment tolerability, recovery, and long-term outcomes. Few studies have examined cancer treatment modality-specific effects on HRF. We examined associations of breast cancer treatment modalities, regimens, and combinations with one-year changes in HRF. <b>Methods:</b> Newly diagnosed early-stage breast cancer patients were recruited between 2012 and 2019 for the Alberta Moving Beyond Breast Cancer (AMBER) cohort study. HRF assessments were completed within 90 days of diagnosis and at one year, including cardiorespiratory fitness, muscle strength and endurance, and body composition. Analysis of covariance was used to test whether HRF changes differed between treatment modalities, regimens, and combinations. All tests were 2-sided. <b>Results:</b> A total of 1350 participants (mean [SD] age, 55.6 [10.7] years) were included. Women who received chemotherapy (n = 797; 59%) experienced statistically significant smaller increases in upper body strength (-1.7 kg, 95% confidence interval [CI]: -3.0 to -0.5), greater declines in lower body endurance (-118.0 kg, 95%CI: -216.6 to -19.3), and greater declines in total lean mass (-0.7 kg, 95%CI: -1.1 to -0.3), bone mineral density (-0.01 g/cm², 95%CI: -0.02 to 0.00), and bone mineral content (0.04 kg, 95%CI: -0.06 to -0.02). Other treatment modalities were modestly and inconsistently associated with HRF changes. Treatment combinations that included chemotherapy had the most negative impact on cardiorespiratory fitness and body composition. <b>Conclusions:</b> Chemotherapy-either alone or in combination with other treatments-had the largest and broadest negative impact on HRF recovery in early-stage breast cancer at one-year follow-up.