Vegan Lifestyle Plus Standard Therapy Drives 99.8% PSA Drop in Metastatic Prostate Cancer

Prostate cancer is the second most diagnosed cancer in men globally, and metastatic disease carries a poor prognosis despite improved systemic therapies. Treatment-related toxicities from androgen deprivation therapy (ADT)—including sarcopenia, metabolic dysfunction, and cardiovascular risk—fuel interest in adjunctive lifestyle interventions that may mitigate side effects and potentially influence disease trajectory.

This case report describes a 60-year-old physically active, lifelong non-smoking Caucasian male from Slovenia with no family history of prostate cancer, who presented with an incidentally discovered PSA of 808.3 µg/L in March 2025. Biopsy confirmed prostate adenocarcinoma with cribriform pattern, Gleason score 9 (4+5), staged cT4N1M1b. Baseline CT showed a dominant 9 × 5.5 cm prostatic mass invading the bladder and seminal vesicles, multiple enlarged pelvic and retroperitoneal lymph nodes, and suspicious osseous lesions. Germline genetic testing revealed no pathogenic variants.

Standard therapy proceeded in stepwise fashion: bicalutamide 150 mg bridging therapy was started April 1, 2025; degarelix (GnRH antagonist) was initiated May 16; enzalutamide 160 mg daily was added July 15; and the patient transitioned to relugolix 120 mg daily on August 8, 2025. Radiotherapy and chemotherapy were discussed but deferred given ongoing PSA response. By personal choice and with nutritional guidance from the first author (a PhD nutritionist), the patient simultaneously adopted a strictly planned whole-food, low-fat (WFLF) vegan diet excluding all animal products, added sugars, refined oils, and ultra-processed foods, providing approximately 2500 kcal/day. He also undertook a structured multimodal exercise program and completed periodic fasting-mimicking diet cycles. Nutritional adequacy was monitored via dietary questionnaires, blood micronutrient measurements, and body composition assessments throughout follow-up.

PSA declined from 808.3 µg/L at baseline to 1.7 µg/L at 11 months, a reduction exceeding 99.8%, and remained suppressed at 14-month follow-up. Follow-up CT at 7 months showed prostate volume reduced to 25 mL with near-complete resolution of local infiltration and regression of lymph nodes. PET/CT with 68Ga-PSMA-11 at 9 months demonstrated uptake only in the prostate and abdominal/thoracic lymph nodes with no bone involvement. Concurrent improvements were documented in body composition, metabolic biomarkers, blood pressure, fiber and micronutrient intake, and reductions in saturated fat and cholesterol.

The authors are explicit that this is a single-patient, descriptive case report and that the independent contribution of the lifestyle intervention cannot be disentangled from the substantial expected PSA response to ADT plus enzalutamide. The case is presented as hypothesis-generating, illustrating the feasibility and apparent safety of a comprehensive integrative oncology approach alongside standard therapy. Controlled prospective trials are needed to determine whether adjunctive vegan lifestyle modification produces measurable oncologic benefit beyond standard-of-care systemic therapy in advanced prostate cancer.