BACKGROUND: Breast cancer (BC) and ovarian cancer (OC) are common female cancers. A proportion of women can be identified as being at increased risk of BC or OC based on genetic and non-genetic factors. Common BC and OC cancer susceptibility genes include BRCA1 and BRCA2, along-with newer moderate penetrance genes such as PALB2, RAD51C, RAD51D, and BRIP1. BC screening, medical prevention, and risk-reducing surgery are recommended risk management strategies. Surgical prevention, including risk reducing mastectomy (RRM) for BC and risk-reducing salpingo-oophorectomy (RRSO) for OC, are the most clinically effective options. Novel approaches like risk-reducing early salpingectomy are under investigation in clinical trials. This thesis aims to evaluate the cost-effectiveness of eligible prevention and screening strategies and the optimal timing of management for BC and OC prevention in the UK. METHODS: This thesis comprises four broad sections: (1) two systematic reviews on the impact of risk-reducing surgery on quality-of-life and its cost-effectiveness for BC and OC prevention; (2) a cost-effectiveness analysis to identify the lifetime BC risk thresholds for offering RRM compared with risk-stratified breast screening; (3) a cost-effectiveness analysis of recommended strategies (RRM, RRSO, breast screening, and medical prevention) for women carrying pathogenic variants (PVs) in high and moderate penetrance BC and OC cancer susceptibility genes; (4) a preliminary cost-effectiveness analysis of the novel two-step surgical prevention strategy for OC– risk-reducing early salpingectomy and delayed oophorectomy (RRESDO)– among BRCA1 and BRCA2 PV carriers, using data from the Preventing Ovarian Cancer through early Excision of Tubes and late Ovarian Removal (PROTECTOR) trial. RESULTS: RRM and RRSO are well-established and clinically effective procedures. Health related quality-of-life following RRM and RRSO remains unchanged, although negative impacts of RRM on body image and of RRSO on sexual function and menopause symptoms are reported. Both RRM and RRSO have been found to be cost-effective compared with non-surgical alternatives primarily among BRCA1 and BRCA2 PV carriers, while the optimal age for surgery varies. The lifetime OC risk thresholds for offering RRSO have been identified as ≥4%–5%. The cost-effectiveness analysis of RRM identified varying lifetime BC risk thresholds for offering this surgery at different ages. Overall, undergoing RRM at common ages of 30 to 55 years appears cost-effective for women with a lifetime BC risk over 35%, which increases to 41% if women experience a longer duration of disutility from surgery. The analysis among women carrying PVs in common BC or OC cancer susceptibility genes indicated that undergoing both RRM and RRSO was cost-effective, maximizing cancers prevented for individuals carrying BRCA1 (RRM at age 30; RRSO at age 35), BRCA2 (RRM at age 35; RRSO at age 40), and PALB2 (RRM at age 40; RRSO at age 45) PVs, while RRSO was cost-effective at age 45 for RAD51C, RAD51D, and BRIP1 PV carriers. The novel approach of RRESDO is cost-saving in preventing OC compared with no surgery among BRCA1 and BRCA2 PV carriers; however, its cost-effectiveness compared with the standard of care of RRSO remains uncertain. CONCLUSIONS: The identified lifetime BC risk thresholds for offering RRM could potentially expand clinical access to RRM beyond BRCA1, BRCA2, or PALB2 PV carriers. Personalizing risk-reducing surgery and counselling for individual cancer susceptibility gene carriers is crucial when considering RRM or RRSO, and these results have informed NICE guidelines. RRESDO may be an acceptable alternative for women reluctant to undergo RRSO, and the analysis should be updated once key parameters regarding OC risk reduction from salpingectomy and the disutility of surgical procedures become available.