<p>The aim of the study was to determine the incidence of chemobrain in breast cancer patients, define it, and review the various tools used to measure it. A comprehensive literature review was performed, and covered all publications up to and including September 30, 2024. Studies were eligible for inclusion if they reported data on chemobrain in adults with breast cancer receiving chemotherapy. The following data were extracted: study characteristics, information on chemobrain, and information on breast cancer treatment. A total of 287 records were identified by the literature search. After eliminating duplicates, irrelevant articles after title and abstract screening, or after full-text review, 11 records were included in the study. The incidence across studies ranged from 9.6 to 81.0%. The pooled incidence of chemobrain was estimated at 39.9% (95% CI 26.3%, 55.2%). Chemobrain appears to affect a significant proportion of breast cancer patients undergoing chemotherapy, with a pooled incidence estimate of approximately 40%. However, the wide range of reported incidences (9.6–81%) suggests that the true prevalence may vary depending on study design, definitions, and assessment tools used.</p>