Background: Rates of both unilateral (UM) and contralateral prophylactic mastectomy (CPM) for early stage breast cancer (ESBC) have been increasing since 2003. Studies suggest that the increase is due to women playing an active role in decision-making. We do not know what factors are influencing the choice for more extensive surgery. Methods: To identify these factors we completed a multi-method study; conducting a systematic review of quantitative literature and qualitative interviews. Decision-making literature was identified from 5 databases and underwent thematic analysis. Purposive sampling identified women across the Toronto Area (Ontario, Canada), who were suitable candidates for breast conserving surgery (BCS) but underwent UM or CPM. Data saturation was achieved after 29 in-person interviews. Constant comparative analysis identified key concepts and themes. Results: ‘Taking control of cancer’ was the dominant theme. Literature illustrated that patients markedly overestimate risk of local recurrence, contralateral cancer and particularly, mortality. Similarly, interviews revealed that fear of breast cancer was expressed at diagnosis and drives the decision-making process. Despite surgeons discussing survival equivalence of BCS and UM, patients chose UM due to fear of recurrence and an overestimated survival advantage. Similarly, patients chose CPM to eliminate contralateral cancer and a misperceived survival benefit. Women were actively trying to Control Outcomes, as more surgery was believed to offer greater survival and therefore greater control. Conclusions: Both the literature and our interviews have illustrated that women seek UM and CPM for treatment of their ESBC to manage their fear of cancer mortality by undergoing more extensive surgery; this in turn drives mastectomy rates. It is important to understand this process so that we may improve our ability to communicate issues of importance to women and facilitate informed decision-making.