Background: Patient-reported outcomes (PROs), including health-related quality of life, are recommended to be routinely collected in clinical trials, but data are limited from trials of sarcoma patients. In this analysis, pooled PRO data are reported from patients with advanced or metastatic soft tissue sarcoma (STS) enrolled to the ANNOUNCE phase III trial of doxorubicin-based therapy. Methods: ANNOUNCE was a phase III trial that randomized 509 patients with STS to receive up to eight cycles of doxorubicin with olaratumab or placebo, followed by single-agent olaratumab or placebo. Dexrazoxane was allowed at any cycle of treatment. Participants completed the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire-Core 30 (EORTC QLQ-C30, which is scored 0–100), and Brief Pain Inventory Short Form Modified (mBPI-sf, scored from 0–10) at each treatment cycle. A descriptive analysis of the longitudinal data was conducted overall and by cumulative dose of doxorubicin received to inform the clinical care of patients with STS. Worsening on the QLQ-C30 was defined as a change of 10 points or more at any post-baseline assessment. Worsening on the mPBI-sf was defined as an increase of ≥2 points from baseline. Results: The majority of participants completed the baseline and at least one subsequent PRO assessment within the trial (n = 460, 90.4% EORTC QLQ-C30; n = 454, 89.2%, mBPI-sf). Patients with STS enrolled to the ANNOUNCE trial had clinically meaningful problems with physical function and pain before initiating doxorubicin. Overall, those with fewer symptoms or better function at baseline received higher cumulative doxorubicin dose throughout the study. At baseline, mean QLQ-C30 fatigue was 29.9 with a median time to first worsening of 0.9 months, and mean nausea/vomiting was 6.5 with 1.4 months until worsening; mean physical function was 78.3 with median time to worsening of 2.1 months and mean health status was 66.8 with median time to first worsening of 1.6 months. Median time to worsening of pain was 7.9 months. Conclusion: Patients with advanced or metastatic sarcoma reported a relatively rapid decline in PROs during doxorubicin-based treatment, with patients with poorer symptoms at baseline (specifically fatigue), subsequently receiving less doxorubicin therapy. The availability of detailed summary data from the patient perspective during doxorubicin-based treatment may inform future care of these patients and can provide a resource for the development of PRO endpoints in future trials.