OBJECTIVES: This study examined the cross-sectional and prospective relationships between subjective (cognitive reappraisal, expressive suppression and experiential avoidance) and objective (high-frequency heart rate variability [HF-HRV]) measures of emotion regulation (ER) and a set of psychological symptoms (anxiety, depression, fear of cancer recurrence [FCR], insomnia, fatigue, pain, and cognitive impairments) among women receiving radiation therapy for non-metastatic breast cancer. DESIGN: Eighty-one participants completed a battery of self-report scales within 10 days before the start of radiotherapy (T1) and within 10 days after its end (T2; approximately 6 weeks after T1). HF-HRV at rest was measured at T1. RESULTS: Canonical correlation analyses revealed that higher levels of experiential avoidance and expressive suppression were cross-sectionally associated with higher levels of all symptoms, except pain, at T1 and at T2 (both p\'s < 0.0001). Higher levels of suppression and reappraisal at T1 were marginally associated with reduced FCR and with increased depression and fatigue between T1 and T2 (p = 0.07). HF-HRV was not associated with symptoms cross-sectionally or prospectively. CONCLUSIONS: Although preliminary, these results are consistent with the hypothesis that maladaptive ER strategies, assessed subjectively, may cross-sectionally act as a transdiagnostic mechanism underlying several cancer-related psychological symptoms.