IRX4 and posterior cortical atrophy: Compared to androgen-responsive cell lines LNCaP, DuCaP and VCaP, androgen-nonresponsive PCa cell lines PC3, 22RV1 and DU145 had a minimal expression of IRX4. Interestingly, overall IRX4 expression was significantly higher in the castration-resistant C42B cell line (a derivative of LNCaP) compared to LNCaP, indicating a role of IRX4 in castration-resistant PCa progression.