on the specific mutation. tubal ligation is a less invasive prophylactic treatment shown to significantly reduce the risk of hgsc. treatment cytoreductive "debulking" surgery may be performed prior to chemotherapy treatment in order to decrease the physical mass of the tumour and thus reduce the number of chemotherapy cycles needed. the typical advanced presentation as well as extra-ovarian spread seen in hgsc can require aggressive debulking procedures. in some cases total abdominal hysterectomy will be performed, in other cases where the patient intends to bear children a salpingo-oophorectomy is performed instead. typical chemotherapy is six cycles of intraperitoneally-delivered platinum-base adjuvant chemotherapy with agents such as carboplatin. measurements of blood ca125 levels are used to determine patient response to the treatment. between 20% and 30% of patients relapse within six months of treatment. poly adp ribose polymerase (parp) inhibitors are another possible treatment, with carriers of brca1/2 mutations being the most responsive epidemiology a study of incidence rates in the us between 1992 and 1999 found that the age-specific incidence rate for hgsc doubles every 10 years up until age 55, where it plateaus at approximately 20 cases per 100,000 women - before dropping dramatically after age 75. ovarian cancer incidence rates are low in east asia and highest in europe, the united states, and australia/new zealand. since 1975, survival rates for ovarian cancer have steadily improved with a mean decrease of 51% by 2006 of risk of death from ovarian cancer for an advanced stage tumour. the increase has mainly been due to successful extended life expectancy of affected patients rather than an improvement in cure rates. a racial disparity exists between black and white women in the us, where black women experience a higher mortality risk from ovarian cancer.