Cognitive dysfunction is increasingly recognized by practitioners and researchers as one of the symptoms that cause great distress for patients with cancer, their families, and their health care providers. The prevalence of cognitive impairment varies and is based on several factors, including the amount of time the patient has had cancer, the type of cancer, the length of treatment, and the treatment used, and is estimated to affect anywhere between 17% and 75% of patients with cancer. In a series of experiments, Wefel et al. noted signs of cognitive impairment in 33% to 35% of cancer patients prior to treatment with chemotherapy and in approximately 61% of patients after chemotherapeutic treatment.

Findings such as these, coupled with the fact that treatment for cancer begins soon after diagnosis, has led to the characterization of chemotherapy-related cognitive impairments as “chemofog” or “chemobrain.” Although the nature of the impairment seems to vary among patients, those who experience chemobrain generally report subtle changes in the ability to maintain focus and engage in routine daily activities. Some investigations performed before and after the initiation of chemotherapeutic treatment find that memory, motor dexterity, and executive function (frontal subcortical components) tend to be impaired, with attention and psychomotor speed remaining unimpaired. Other studies have shown that working memory, or the ability to process information and do multiple tasks, is often impaired, whereas hippocampal components of memory, such as retention and consolidation, frequently are not.