Background <p>“Textbook outcome” is an increasingly utilized composite metric used to assess postoperative outcomes in surgical oncology. Variability in “textbook outcome” definitions hampers its reliability and comparability. This systematic review investigates the heterogeneity in “textbook outcome” definitions and advocates for standardization.</p> Materials and Methods <p>PubMed was systematically searched for English language studies published between 2018 and 2023 reporting “textbook outcome” in cancer surgeries. Data on “textbook outcome” definitions and component parameters, including mortality, complications, hospital stay, and readmission was independently extracted. These results were screened for exclusion and independently reviewed by the research team in a standardized fashion. A secondary analysis was performed to assess discrepancies across reviewers with reconciliation of review variation. Descriptive statistics were used to analyze variability across studies.</p> Results <p>A total of 86 papers were included, encompassing 116 disease-specific studies. No component was included in all studies, mortality (88.8%), complications (90.5%), readmission (93.1%), and length of stay (89.7%) were most commonly included. Component definitions varied widely: mortality was variably defined as in-hospital, 30-day, or 90-day mortality, while complications ranged from Clavien–Dindo graded to undefined. Timeframes and thresholds for metrics such as readmission and length of stay also varied widely. Many studies lacked clarity, requiring inference to deduce “textbook outcome” definitions, highlighting a need for standardized reporting.</p> Conclusions <p>Despite its potential as a comprehensive quality indicator, “textbook outcome” definitions currently suffer from significant definitional heterogeneity. Standardized, procedure specific “textbook outcome” definitions and reporting guidelines are needed to improve its interpretability, comparability, and clinical applicability.</p>