Standard Therapy Plus Adjunctive Vegan Lifestyle Intervention in Metastatic Prostate Cancer: A Case Report.

Prostate cancer is among the most frequently diagnosed cancers in men globally, with metastatic disease contributing substantially to morbidity and mortality. While conventional therapies remain the standard of care, dietary and lifestyle behaviors are increasingly explored as potentially modifiable factors influencing clinical outcomes, although their role in advanced disease is not well established. We report a 60-year-old, physically active male, lifelong non-smoker without significant comorbidities, diagnosed with de novo metastatic prostate adenocarcinoma (Gleason score 9) and an initial prostate-specific antigen (PSA) of 808.3 µg/L. The patient received standard androgen deprivation therapy. By personal choice, he adopted a whole-food, low-fat (WFLF) vegan diet, structured physical activity, and periodic fasting-mimicking diet cycles. These interventions complemented, but did not replace or delay, conventional treatment. During the 14-month follow-up period, serial PSA measurements, laboratory tests, blood pressure monitoring, dietary assessment, body composition analysis, imaging, and germline genetic testing were performed. PSA declined from 808.3 µg/L to 1.7 µg/L (>99.8%), and remained suppressed throughout follow-up. Concurrent improvements were observed in body composition and metabolic biomarkers. The WFLF vegan diet increased fiber and micronutrient intake while reducing saturated fat and cholesterol. This case demonstrates the successful application and execution of an integrative oncology approach and highlights metastatic prostate cancer managed with standard therapy alongside patient-initiated lifestyle modifications. The findings should be interpreted as descriptive, exploratory, and hypothesis-generating. Given the single-patient design, the independent impact of lifestyle interventions cannot be determined. Controlled studies are warranted to clarify their potential role in advanced prostate cancer management.