PURPOSE: Reducing recurrence and mortality is crucial for breast cancer survivors. We investigated the effects of a 12-week resistance training (RT) versus high-intensity interval training (HIIT) program on myokines, cytokines secreted by skeletal muscle cells at rest in response to muscle contraction, and cancer cell inhibition. METHODS: Twenty-eight survivors of breast cancer (age 55.5 +/- 8.8 yr, body mass index 27.9 +/- 5.1 kg/m2, time since diagnosis 31 +/- 12.3 months) were randomly allocated to a 12-week supervised moderate to high intensity RT (n = 14) or HIIT (n = 14) program 3 days per week. Resting blood was collected before and post exercise program (at least 48 hours before the first and after the last exercise session) to measure serum levels of myokines (decorin, interleukin 6 (IL-6), secreted protein acidic and rich in cysteine (SPARC), and oncostatin M (OSM)) and triple negative MDA-MB-231 cell growth in vitro, using real time cellular analysis to determine growth rate. RESULTS: Exercise attendance was 85% for RT and 81% for HIIT. Serum levels of SPARC for RT and OSM for HIIT significantly (p < 0.05) increased (11 to 15%) after 12 weeks, with no significant differences between groups. MDA-MB-231 cell growth was significantly (p < 0.05) reduced for both RT and HIIT by 22% and 25%, respectively, with no significant difference between groups. Reductions in MDA-MB-231 cell growth in HIIT were associated with improvements in lean and fat mass. CONCLUSIONS: A program of RT or HIIT can increase levels of myokines (an effect considered beneficial given their potential cancer-suppressive effects) and inhibit growth of MDA-MB-231 cells in survivors of breast cancer. In addition, development of the anti-tumor environment may be mediated by exercise-related changes in muscle strength and body composition.

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