Post-chemotherapy cognitive impairment (also known as chemotherapy-inuced cognitive dysfunction, chemo brain or chemo fog) describes the cognitive impairment that can result from chemotherapy treatment. Approximately 20-30% of people who undergo chemotherapy experience some level of post-chemotherapy cognitive impairment. The phenomenon first came to light because of the large number of breast cancer survivors who complained of changes in memory, fluency, and other cognitive abilities that impeded their ability to function as they had pre-chemotherapy.