PTEN and breast cancer: In BRCA1-associated breast cancer, which has molecular similarities with HGSOC (e.g., genomic instability, chromosomal complexity, frequent TP53, BRCA1 and BRCA2 mutation), PTEN loss was also the most frequent initiating event.18 Interestingly, we found here that the frequency of HGSOC cases with heterogeneous expression of PTEN (suggestive of a later sub-clonal loss of PTEN) is higher in more advanced disease in patients without any confirmed pathogenic BRCA1/2 mutation.