 Decreased rates of homologous recombination cause inefficient DNA repair , which can also lead to cancer . This is the case with BRCA1 and BRCA2 , two similar tumor suppressor genes whose malfunctioning has been linked with considerably increased risk for breast and ovarian cancer . Cells missing BRCA1 and BRCA2 have a decreased rate of homologous recombination and increased sensitivity to ionizing radiation , suggesting that decreased homologous recombination leads to increased susceptibility to cancer . Because the only known function of BRCA2 is to help initiate homologous recombination , researchers have speculated that more detailed knowledge of BRCA2 's role in homologous recombination may be the key to understanding the causes of breast and ovarian cancer . 
