Background: Taxane-based regimes has improved survival in early breast cancer and now is used routinely. A common side effect is oedema which potentially increases the risk of lymphoedema in the arm after surgery. This has not been assessed prospectively. The aim of this study was to determine the effect of taxane-based regimens on extracellular fluid (ECF) in the arm on the side of surgery. Methods: Women (n=441) aged 56.8 (SD 11.2) years enrolled prior to surgery for early breast cancer and were reassessed within 1 month and 6, 12, and 18 months following surgery. Assessment included bioimpedance spectroscopy which quantifies ECF in each arm and used to derive the ECF ratio. Based on the ECF ratio, women were categorised as having, or not, swelling preferentially in their at risk arm at each time point and having no taxane-based chemotherapy (n=269), paclitaxel (n=73) or docetaxel chemotherapy (n=88). Results: Pre-surgery, the ECF ratio was not significantly different in women who later did or did not receive taxane-based chemotherapy. Following surgery but prior to commencing chemotherapy, 45 (11%) women had increased ECF in their at-risk arm. Both taxane-based chemotherapies and elevated postoperative arm swelling were associated with swelling at each follow-up timepoint (Table). Conclusions: In addition to pre-existing swelling, both taxel chemotherapies were associated with swelling preferentially in the at-risk arm between 6 and 18 months following surgery. Strategies to prevent or minimise this swelling need to be developed.