An international team of researchers say that one way BRCA1 mutations cause cancer is by knocking out PTEN a tumor suppressor gene. This is the second most mutated gene in cancer after p53.
The scientists made the connection between BRCA1 and PTEN using techniques to search for physical chromosome breaks within the PTEN gene. Previous searches for PTEN mutations in BRCA1 tumors looked for conventional mutations and failed to turn up any abnormalities, report the investigators.
The team scanned 34 biopsies taken from women with BRCA1 tumors. The PTEN gene had been split in two but inadequately repaired in about one-third of the cancers. In some cases, entire sections of the gene were missing; in others, one-half of the gene was reattached to other regions on the chromosome.
These types of large chromosomal mistakes stem directly from the tumor’s lack of BRCA1, a gene that is normally involved in the repair of such damage. In breast cancers from women with normal BRCA1, such large mutations in PTEN were rarely detected, according to the investigators.
The study was published online in Nature Genetics on December 9. The research was performed by investigators at Columbia University, Lund University, the University of Tampere, Mediterranean Institute of Oncology, Karmanos Cancer Institute, and Seinäjoki Central Hospital.