Abstract Background Few data are available in the literature regarding chemotherapy dosage adjustment in obese patients. Docetaxel is a lipophilic substance, highly bound to albumin; obesity might result in an accumulation of docetaxel and may lead to a higher rate of toxicity. The objective of this study was to assess the tolerance to docetaxel in obese and non obese patients, according to their body mass index (BMI). Methods A retrospective study was carried out. Patients were divided according to their BMI, considering a limit of 30 kg/m2. All patients received docetaxel (100 mg/m2) as a part of adjuvant chemotherapy for breast carcinoma. Toxicity of docetaxel such as neutropenia, hand-foot syndrome, mucositis, and neuropathy were assessed in both groups. Patients receiving concomitant therapies leading to similar adverse events were excluded (e.g. cyclophosphamide, 5-FU, …). The included patients received docetaxel alone or in association with trastuzumab or bevacizumab. Qualitative data analysis was performed using Fisher's exact test. Quantitative data were studied using the Student test. Results Among the 49 patients, 18 (37%) presented with a BMI > 30 kg/m2. The median age was 53 years-old in the group BMI > 30 and 55 years-old in the group BMI < 30 (p = 0.9383). The median dose intensity delivered was 91% (74-100%) in the group BMI> 30 and 97.7% (75-100%) in the group BMI < 30 (p = 0.06). The median value for albumin was 75 g/L (59-86 g/L) in the BMI > 30 and 71 g/L (56-79 g/L) in the BMI < 30 (p = 0.122). Toxicity in both groups was as follows: No neuropathy was observed in both groups. Conclusions Obese patients (BMI > 30 kg/m2) presented with more toxicities (p = 0.013). Hypoalbuminemia did not represent a risk factor for toxicity in this study as patients had normal albumin levels. Obesity is a risk factor for toxicity in patients treated with docetaxel. Dosage calculation according to body surface area is not suitable for these patients. Toxicity in the group BMI < 30 seems to demonstrate greater susceptibility to the molecule for these patients. Further studies will try to identify the different mechanisms of toxicity of docetaxel involved obese patients, including the interaction between docetaxel and fats. Measures have also to be taken to obtain a favorable effectiveness/toxicity balance in obese patients. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P4-14-04.