Background: Prolongation of survival and maintenance of quality of life (QoL) are the primary therapeutic goals in advanced breast cancer. Around 10% of adverse events (AEs) in the CTCAE are symptomatic AEs (e.g., nausea, sensory neuropathy), which can severely and directly affect the QoL of patients. However, seldom evidence mapped the QoL and symptomatic AEs utilizing patient-reported outcomes (PROs) in heavily pretreated breast cancer patients. This study aimed to investigate the PROs for measuring the QoL and symptomatic AEs of advanced breast cancer treated with third-line and beyond chemotherapy-based regimens in China. Methods: This national survey enrolled patients with advanced breast cancer receiving third-line and beyond chemotherapy-based regimens in 59 centers all over China from March to April in 2021. Each patient filled out a questionnaire containing demographic information, medical history, EORTC-QLQ-C30, and symptomatic AEs. The symptomatic AEs included fatigue, nausea/vomiting, pain, dyspnea, insomnia, appetite loss, constipation, diarrhea, alopecia, fever, and limb numbness. The range method was used for the linear conversion of the PRO scores, which were converted into standardized scores of 0 to 100. Results: This study enrolled 1015 patients with the median age of 52 years. The QoL of all patients were poor, with the global health status score of 52.4±17.7 (Table). All the symptomatic AE scores were low among the patients. However, no significant differences were observed in global health status and symptomatic AEs between mono-chemotherapy and multi-agent chemotherapy (All P>0.05). Conclusions: The QoL of advanced breast cancer patients treated with third-line and beyond chemotherapy were poor, especially in symptomatic AEs. In addition, the EOTRC-QLQ-C30 scale appears to underestimate the differences in symptomatic AEs between mono-chemotherapy and multi-agent chemotherapy, probably due to a lack of sensitivity of the scale, which fails to match the actual clinical observations of the PROs and QoL. Therefore, new scales need to be developed for the evaluation of symptomatic AEs and QoL in advanced breast cancer.