Cancer-related hot flashes are often a lasting and distressing side effect of hormone-blocking therapies that are most often experienced by women with breast cancer and men with prostate cancer treated with these therapies. Hot flashes have been defined as a sensation of heat that may be accompanied by facial flushing, perspiration, chills, heart palpitations, night sweats, and feelings of anxiety. The frequency and intensity of hot flashes can cause fatigue and sleep disturbances that diminish quality of life and reduce adherence with prescribed therapies that block estrogens or androgens. Hot flashes are reported to be significantly more frequent and severe in women treated for breast cancer than in women undergoing natural menopause. They also commonly occur in men treated for prostate cancer with surgical or chemical castration to block the synthesis of androgens that can fuel cancer growth.