ObjectiveTo identify whether there is an association between body composition phenotypes and toxicity to chemoradiotherapy in women with cervical cancer. MethodsThis is a prospective cohort study that included 330 adult patients with cervical cancer treated with chemoradiotherapy. Computed tomography images were used to quantify skeletal muscle index (SMI) and radiodensity (SMD), total adipose tissue index (TATI), and visceral adipose tissue index (VATI). Chemoradiotherapy toxicity was assessed weekly, and toxicity-induced modification of treatment (TIMT) was considered as any severe adverse event resulting in treatment interruption, delay, or dose reduction. ResultsApproximately 45% presented at least one unfavorable body composition parameter (low SMI, low SMD, high TATI or high VATI), 23% had two conditions, and 3% had three conditions. The incidence of toxicity ≥ grade 3 and TIMT was 55% and 30%, respectively. For adverse events ≥ grade 3, low muscle mass was the determining factor for worse outcomes when evaluated alone or in phenotypes with low SMD and normal adiposity. All body composition phenotypes were associated with TIMT, increasing the risk when both conditions were present [RR=5.21(1.96–13.85), p<0.001]. ConclusionsLow muscle mass was an independent factor for the higher number of adverse events, as it remained a risk factor when analyzed in isolation or in association with adipose tissue. Women with excess adipose tissue associated with low muscle mass had a risk approximately 4 times higher of delaying or interrupting chemoradiotherapy. Furthermore, for the sum of unfavorable conditions, there was a progressive increase in the risk of TIMT.