Background: Health-related quality of life (QoL) is a self-assessed construct indicating how people feel in regard to aspects of their health. Performance status (PS) is evaluated by the treating physician. We examined whether pretreatment QoL and PS are related to subsequent treatment discontinuation and treatment changes in high-risk breast cancer patients receiving chemotherapy. Methods: We conducted a prospective cohort study with data from a randomized phase III trial comparing FEC- and EC-DOC-chemotherapy in patients with primary breast cancer (ADEBAR). We examined the patient’s request to discontinue the study, discontinuation due to toxicity, the prolongation of therapy, and dose reduction. Baseline QoL was assessed using the EORTC QLQ-C30. PS was evaluated using the Eastern Cooperative Oncology Group Scale (ECOG). Four QoL scales were selected prior to analysis as outcomes: global health, physical functioning, emotional functioning, and fatigue. Multivariate binary logistic regression analyses were used to test for differences within the independent variables. Main results: 1322 patients were included. 1094 (82.8 %) patients completed therapy according to protocol. 6.3 % stopped therapy due to toxicity and 4.4 % refused treatment. Global health was not related to any of the four QoL outcomes. Physical functioning had the strongest impact on QoL, when comparing the fittest group to the lowest quintile [OR 2.14 (95 % CI 1.00–4.60)]. ECOG 0 compared to worse than 1 was strongly correlated to therapy discontinuation due to toxicity [OR 20.15 (95 % CI 9.48–42.83)] and treatment refusal [OR 8.32 (95 % CI 3.81–18.14)]. Conclusions: Pretreatment QoL, especially physical functioning, is associated with subsequent therapy discontinuation due to toxicity and with changes of the treatment protocol. Pretreatment performance status is strongly associated with therapy discontinuation due to toxicity and with treatment refusal.