Among genes known to be related to human breast cancer [27], we previously reported the reduced expression of Pten (on 1q52, 0.53-fold), Pik3r1 (on 2q12, 0.61-fold), and Map3k1 (on 2q14, 0.75-fold) in mammary carcinomas of (SD×COP)F1 rats [22]. Here, PIK3R1 is linked to breast cancer.