PTEN and neoplasm: In the prostate of PTEN-knockout mice, much relaxed layers of smooth muscle actin (SMA)-positive malignant epithelial cells surrounding stroma are demonstrated, while a highly condensed layer of SMA-positive stroma, useful against the invasion of tumor cells into the adjacent stromal tissue, was detected in the prostate of wild-type mice (see Figure 3, point 6) [24].