Aim: To evaluate the association between baseline comprehensive geriatric assessment (CGA) or the Groningen Frailty Indicator (GFI) and toxicity in elderly metastatic breast cancer (MBC) patients treated with first-line palliative chemotherapy. Patients and methods: MBC patients (>= 65 years) were randomized between pegylated liposomal doxorubicine or capecitabine. CGA included instrumental activities of daily living (IADL), cognition using the mini-mental state examination (MMSE), mood using the geriatric depression scale (GDS), comorbidity using the Charlson index, polypharmacy and nutritional status using the body mass index. Frailty on CGA was defined as one or more of the following: IADL <= 13, MMSE <= 23, GDS >= 5, BMI <= 20, >= 5 medications or Charlson >= 2. The cut-off for frailty on the GFI was >= 4. Results: Of the randomized 78 patients (median age 75.5 years, range 65.8-86.8 years), 73 were evaluable for CGA; 52 (71%) had one or more geriatric conditions. Grade 3-4 chemotherapy-related toxicity was experienced by 19% of patients without geriatric conditions compared to 56% of patients with two geriatric conditions and 80% of those with three or more (p = 0.002). Polypharmacy was the only individual factor significantly associated with toxicity (p = 0.001). GFI had a sensitivity of 69% and a specificity of 76% for frailty on CGA, and was not significantly associated with survival or toxicity. Conclusion: In this study of elderly patients with MBC, the number of geriatric conditions correlated with grade 3-4 chemotherapy-related toxicity. Therefore, in elderly patients for whom chemotherapy is being considered, a CGA could be a useful addition to the decision-making process. (C) 2013 Elsevier Ltd. All rights reserved.