The Renal Insufficiency and Anticancer Medications (IRMA) study is a French national, observational study which demonstrated the high prevalence of abnormal renal function in a population of 4,684 solid tumour patients. Among them, 50-60% had decreased renal function defined as CrCl below 90 and 80% were treated with anticancer drugs that either necessitated dosage adjustment in case of RI or were potentially nephrotoxic drugs. Since patients and drugs used differ depending on the type of tumour, the IRMA Study Group started analyses in different subgroups of patients. In the 1898 IRMA patients with breast cancer, the prevalence of RI was still very high in spite of a normal serum creatinine in almost all cases. Some anticancer drugs, as in particular some bisphosphonates, capecitabine and platinum salts, may be nephrotoxic and/or need dosage adjustment. However other important drugs in breast cancer do not require dose reduction, and do not present with potential nephrotoxicity (anthracyclines, taxanes, trastuzumab). Both issues seem to be slightly but significantly more important in patients with bone metastases as compared to patients with a non-metastatic disease.