Could the non-mutated copy of BRCA actually help cancer cells survive?
To understand what might be causing this phenomenon, we need to know how BRCA works. BRCA is normally a gene that codes for a cell’s self-maintenance, giving it the ability to repair its own DNA. The platinum-based chemotherapies often used to treat ovarian cancer work by damaging the DNA of cancer cells, causing them to die.
When carrying two mutated BRCA alleles and fulfilling the double-hit hypothesis, the cancer cells have presumably lost both genes that give it self-repairing ability. For this group, platinum chemotherapies can effectively damage DNA and the cancers expectedly die because they can’t repair their genome.
Cancer patients who still have one normal copy of BRCA still have some DNA repair ability. The gene might be giving cancer cells the ability to repair any damage caused by the platinum chemotherapy. This explains why we see such unique resistance in ovarian tumors that still carry one normal BRCA allele.