PTEN and maternal uniparental disomy of chromosome 20: In fact, of the TNBCs from The Cancer Genome Atlas breast cancer study, approximately 10% of cases harbor amplification or somatic mutations in PIK3CA and 8% harbor homozygous deletions or somatic mutations in PTEN. 38 Therefore, these recurrent alterations affecting PI3K pathway-related genes are unlikely to explain the unique histologic features of MBCs.