A 60-year-old man, with a background history of insulin dependent diabetes, after a treated Escherichia coli urinary tract infection (Amoxicillin-Clavulanic acid for 10 days), experienced symptom recurrence. His main symptoms included feeling unwell, burning in urination and pelvic pain. A digital rectal examination revealed a tender swelling in the pelvic area. His prostate-specific antigen (PSA) was 0.8 ng/mL, while the 2-glass Meares-Stamey test was negative. A magnetic resonance imaging (MRI) of his pelvis identified a large unusual appearing mass replacing both the prostate and seminal vesicles (Fig. 1). Rest of the imaging (computed tomography of chest, abdomen, pelvis and bone scan) showed a few small volume pelvic side-wall lymph nodes and no evidence of lung or other distant metastases. Given the imaging appearances, a prostatic sarcoma, such as a leiomyosarcoma, was felt to be more likely than a prostate adenocarcinoma. The mass was biopsied treansrectally with the histology showing xanthogranulomatous prostatitis (Supplementary Fig. 1). Repeat MRI performed 10 months later following antibiotic treatment (Ciprofloxacin for 6 weeks) showed dramatic resolution of the mass with almost normal appearance of the prostate gland (Fig. 2).