SYP and metastatic neoplasm: Needle biopsy confirmed a metastatic tumor with squamous differentiation that was CK5/6-positive and chromogranin A-, synaptophysin-, and androgen receptor-negative.<h4>Conclusion</h4>We encountered a case of double-negative prostate cancer with squamous differentiation identified by needle biopsy of a right ilium metastasis after abiraterone, enzalutamide, and docetaxel failure.