Docetaxel is an antineoplastic drug from the taxane family that inhibits tubulin polymerization. Its brand name is Taxotere. In mid-2010, the formulation of Taxotere changed from a two-vial preparation needing a predilution (T2V) to a one-vial ready-to-use preparation (T1V). The aim of this study was to compare the toxicity profile of these two formulations. This retrospective observational and monocentric study included all patients who received Taxotere-based chemotherapy (100 mg/m) as an adjuvant or a neoadjuvant treatment for localized breast cancer, following initial treatment with anthracycline-based chemotherapy. Patients received either T2V or T1V Taxotere depending on the period of treatment. The main endpoint was the ratio of the dose of Taxotere received to that scheduled (R=docetaxel dose received/docetaxel dose scheduled). The secondary endpoint was tolerance. A total of 97 patients were included: 39 in the T2V group and 58 in the T1V group. The ratio of docetaxel received/docetaxel scheduled was significantly lower in the T1V than in the T2V group (0.83 vs. 0.95, respectively; P=0.028). A higher proportion of patients did not receive the totality of the scheduled dose in the T1V than in the T2V group (28 vs. 8%, respectively; P=0.03). Furthermore, the proportion of patients experiencing cutaneous toxicity was significantly higher in the T1V than in the T2V group (50 vs. 15%, respectively; P<0.001) as well as for neurological toxicity (31 vs. 15%, respectively; P=0.03). The frequency of grade 3 toxicities was higher in the T1V than in the T2V group (50 vs. 8%, P=0.016). The frequency of idiosyncratic toxicities was not affected by the change of formulation (4.7 vs. 5.4%, P=0.98). This study shows that patients treated with the T1V formulation received a significantly smaller dose of Taxotere than patients treated with T2V. In this small retrospective study, no conclusions can be drawn as to why a change in formulation would be associated with differences in dose tolerance. However, it does encourage caution and need for clinical data analysis when adopting even minor changes in the formulation of well-known anticancer drugs.