Nulliparity is consistently associated with an increased risk of ovarian cancer, including among BRCA1/BRCA2 mutation carriers. Risk may also be increased among women who have used fertility drugs, especially those who remain nulligravid.[63,67] Evidence is growing that the use of menopausal HRT is associated with an increased risk of ovarian cancer, particularly in long-time users and users of sequential estrogen-progesterone schedules.[68,69,70,71]
Bilateral tubal ligation and hysterectomy are associated with reduced ovarian cancer risk,[63,72,73] including in BRCA1/BRCA2 mutation carriers. Ovarian cancer risk is reduced more than 90% in women with documented BRCA1 or BRCA2 mutations who chose risk-reducing salpingo-oophorectomy (RRSO). In this same population, prophylactic removal of the ovaries also resulted in a nearly 50% reduction in the risk of subsequent breast cancer.[75,76] (Refer to the Risk-reducing salpingo-oophorectomy section of this summary for more information about these studies.)
Use of OCs for 4 or more years is associated with an approximately 50% reduction in ovarian cancer risk in the general population.[63,64] A majority of, but not all, studies also support OCs being protective among BRCA1/ BRCA2 mutation carriers.[66,77,78,79,80] A meta-analysis of 18 studies including 13,627 BRCA mutation carriers reported a significantly reduced risk of ovarian cancer (SRR, 0.50; 95% CI, 0.33–0.75) associated with OC use. (Refer to the Oral contraceptives section in the Chemoprevention section of this summary for more information.)
Models for Prediction of Breast Cancer Risk
Models to predict an individual's lifetime risk of developing breast cancer are available.[81,82] In addition, models exist to predict an individual's likelihood of having a BRCA1 or BRCA2 mutation. (Refer to the Models for prediction of the likelihood of a BRCA1 or BRCA2 mutation section of this summary for more information about these models.) Not all models can be appropriately applied for all patients. Each model is appropriate only when the patient's characteristics and family history are similar to the study population on which the model was based. Different models may provide widely varying risk estimates for the same clinical scenario, and the validation of these estimates has not been performed for many models.[82,83] Table 1 summarizes the salient aspects of two of the common risk assessment models and is designed to aid in choosing the model that best applies to a particular individual.
The Claus model [84,85] and the Gail model  are widely used in research studies and clinical counseling. Both have limitations, and the risk estimates derived from the two models may differ for an individual patient. Several other models, which include more detailed family history information, are also in use and are discussed below.