PTEN and breast cancer: PTEN loss is highly associated with BRCA1 breast cancers (28 (82.4%) of 34 of tumor samples from BRCA1 carriers showed the loss of PTEN by immunohistochemistry) and can result from gene rearrangements involving DNA double-strand breaks, intragenic inversions on insertions, homozygous deletions, and focalized CNIs [8].