Original Publication Date: 25 February, 2016
Publication / Source: Oncology Central
Authors: Samuel G Smith
Breast cancer is the most common female cancer and the leading cause of death in women under 40 years of age . Improved treatments have increased breast cancer survival over the past few decades, but incidence continues to rise . Primary prevention of the disease is required to address this trend and reduce overall burden in the population.
Several primary prevention options are available to women, depending on their individual level of risk and personal preference. Adherence to recommended lifestyle behaviors such as limiting alcohol consumption and increasing physical activity remains a primary goal for women at population risk, while surgical intervention is offered to carriers of deleterious mutations in genes such as BRCA1 and BRCA2. However, for women with a moderate family history risk that does not warrant surgical intervention, or for those who decline the offer of surgery, chemoprevention remains an option.
Several chemoprevention trials have demonstrated the efficacy of selective estrogen-receptor modulators (SERMs) in preventing breast cancer. A meta-analysis of nine SERM trials demonstrated a 51 % risk reduction in estrogen-receptor positive (ER+) breast cancer, which is a reduction in overall disease burden of at least one third . SERMs were shown to increase the risk of venous thromboembolic events, endometrial cancer and menopausal side-effects. Long-term observation of the International Breast Intervention Study (IBIS) trial demonstrated the preventive effect of tamoxifen lasts at least 20 years, but further follow-up is needed before mortality effects are known . Aromatase Inhibitors (AIs) such as anastrozole  (IBIS 2 trial) and exemestane  (MAP.3 trial) have also been effective at reducing breast cancer incidence among postmenopausal women, and may offer an alternative option for women who cannot tolerate SERMs. However, long-term mortality outcomes will only be available from the IBIS 2 trial, as the MAP.3 trial was unblinded at 35 months.
In 2013, the UK National Institute for Health and Care Excellence (NICE) released guidance suggesting women at increased risk of breast cancer should be offered tamoxifen and raloxifene as part of routine clinical care . This follows similar recommendations in 1999 and 2007 from the US FDA to approve the prophylactic use of tamoxifen and raloxifene, respectively. Since these announcements, attention has started to focus on the acceptance of these agents to the population, as well as their continued use over time. The strengths and limitations of SERMs and AIs makes the decision to initiate chemoprevention a challenging process for patients and clinicians alike.