Background: Body composition metrics as predictors of adverse events are a growing area of interest in oncology research. One barrier to the use of these metrics in clinical practice is the lack of standardized cut points for identifying patients with at-risk body composition profiles. We examined the association of chemotherapy adverse events with several body composition measures, using alternative cut points from published studies. Methods: This is a retrospective study of women diagnosed with early breast cancer (EBC). Axial computerized tomography (CT) images from lumbar L3 segments were analyzed for the following body composition measures: myosteatosis (low Skeletal Muscle Density/SMD), sarcopenia (low Skeletal Muscle Index/SMI), and high Visceral Adipose Tissue (VAT). Adverse events during chemotherapy were dose reduction, early treatment discontinuation, and hospitalization. Log-binomial modeling was used to evaluate associations between body composition measures at different cut points with adverse events, adjusting for age, race, Body Mass Index/BMI, and comorbidities. Relative risks were reported as the measure of association. Results: In a sample of 338 women, mean age was 51, 14% were age 65 or older, 32% were non-white, 40% had obesity (/BMI ≥ 30 kg/m2), and mean number of comorbidities was 1.56. In multivariable analysis (MV), all three SMD cut points for myosteatosis had significant associations with total number of adverse events, as well as different cut points having significant associations with either dose reduction, early treatment discontinuation or hospitalization. SMI and VAT were not significant in the MV analysis; however, in some models, age and total comorbidities were significant for adverse events. Conclusions: Among CT-derived measures of body composition, myosteatosis determined at any of three SMD cut points was associated with total and individual adverse events during chemotherapy for early breast cancer.