KLK3 and prostate cancer: Double-negative tumors can convert to the squamous phenotype.<h4>Case presentation</h4>A 62-year-old man was newly diagnosed with prostate cancer (serum prostate-specific antigen 2613 ng/mL, Gleason score 4 + 5 = 9, cT3aN1M1b) that progressed to castration resistance 4 months after starting abiraterone with androgen deprivation therapy.