Introduction: Breast cancer remains one of the most prevalent malignancies among women and a leading cause of cancer-related mortality in Honduras. Beyond medical treatment, patients’ quality of life is significantly impacted in physical, emotional, social, and nutritional domains—areas often overlooked in outpatient care. Objectives: To implement and evaluate the effectiveness of a comprehensive intervention plan aimed at improving the quality of life of women diagnosed with breast cancer attending outpatient oncology services at Hospital San Felipe in Tegucigalpa, Honduras. Material and Methods: A quasi-experimental pre-post study without a control group was conducted. The population consisted of 31 patients diagnosed with breast cancer. The intervention included nutritional assessment and counseling, physical activity recommendations, psychological support, and clinical follow-up. The EORTC QLQ-C30 questionnaire was administered to measure cancer-related quality of life. Results: Pre-intervention, patients had mean physical and emotional functioning scores of 52.3 ± 14.7 and 45.6 ± 16.2, respectively, with a high symptom burden of fatigue (67.1 ± 18.0). After the intervention, significant improvements were observed in physical functioning (68.4 ± 12.5; p = 0.003), emotional functioning (62.5 ± 14.9; p = 0.008), and global quality of life (from 48.2 ± 20.5 to 66.9 ± 18.1; p = 0.002), as well as a significant reduction in fatigue (51.7 ± 17.4; p = 0.015). Likewise, significant increases were seen in appetite (p = 0.010) and treatment adaptation (p = 0.005). Conclusions: The intervention plan proved feasible and effective in improving quality of life for outpatient breast cancer patients. Institutional adoption of this model is recommended to strengthen holistic oncology care in similar settings.