Expression of the PTEN tumor suppressor is frequently lost in breast cancer in the absence of mutation or promoter methylation through as yet undetermined mechanisms.

• PTEN肿瘤抑制因子在乳腺癌中虽常呈失表达，但并不是通过基因突变或促进子甲基化而实现的，因此其失表达的机制还不清楚。