Objectives Aggregation is one of the key critical points limiting the stability of monoclonal antibodies in solution. The present study aimed to investigate the in-use stability of a residual monoclonal antibody solution after withdrawal of most of the filling volume of PF-06439535 (bevacizumab biosimilar), addressing the physical and chemical stability with respect to aggregation and fragmentation. Methods The stability of residual PF-06439535 solution (25 mg/mL) after withdrawal of 80% (12.8 mL) filling volume with a 20G needle was monitored over a light-protected storage period of 8 days at 2-8°C and 25°C with measurement time points at D0 (start of storage), D2, D4, and D8 (2, 4, and 8 days of storage after start, respectively). Unopened vials stored under the same conditions served as control. For this purpose, the analytical results from size exclusion chromatography, dynamic light scattering, and micro-flow imaging obtained after the individual measurement time points up to 8 days were compared with those obtained at D0 and with those obtained for unopened vials stored under the same conditions. Results No aggregation or ongoing fragmentation due to partial withdrawal of filling volume could be observed in the residual PF-06439535 solution. Moreover, no changes in the particle size distribution at D8 compared with the D0 values were identified upon storage at either 2-8°C or 25°C (both opened and unopened vials). The total concentration of particles ≥10 µm of all samples was <100 particles/mL. In addition, no variations in the pH values or in the visual appearance were detected over the whole study period in all samples at all storage conditions. Conclusions Consequently, residual PF-06439535 solution (25 mg/mL) in opened vials may be regarded as stable when stored light-protected over a period of 8 days in the refrigerator (2-8°C) or at 25°C. HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY⇒ There is a strong interest in clinical practice in the stability of residual PF-06439535 concentrate in opened vials. Based on the generated extended stability data obtained in the present study, the stability of PF-06439535 should be verified in more extensive studies.