The pooled OR from 3 studies including 71 of DCIS and 124 of normal breast tissues are shown in Fig. 2A (odds ratios, OR = 22.30, 95% confidential intervals, CI = 1.98–251.51, P = 0.01), which demonstrates that loss of PTEN expression by hypermethylation plays a critical role in the early tumorigenesis of DCIS. Here, PTEN is linked to ductal breast carcinoma in situ.