We previously reported aberrations of genes related to the phosphoinositide 3-kinase (PI3K) pathway, including downregulation of Pten (1q52) and mutations of Pik3r1 (2q12), in mammary cancers from the same cohort of irradiated (SD×COP)F1 rats [22], but the frequency of these mutations was low (i.e., 1 of 14 for each mutation). Here, PIK3R1 is linked to breast cancer.