TK1 and posterior cortical atrophy: By contrast, genes related to cell cycle and DNA replication such as cell division cycle 45-like (CDC45L), checkpoint kinase 1 (CHEK1), and thymidine kinase 1, soluble (TK1) were among the most significantly downregulated genes in 3D spheroids, suggesting that PCa cells exhibit strong cell-to-cell and cell-to-ECM interactions but a low proliferative activity in 3D compared to 2D culture.