Influence of Exceptional Patient Characteristics on Everolimus Exposure

Inclusion Criteria: * Adult women (≥ 18 years of age) with metastatic or locally advanced breast cancer not amenable to curative treatment by surgery or radiotherapy. * Histological or cytological confirmation of estrogen-receptor positive (ER+) breast cancer * Postmenopausal women * Radiological or clinical evidence of recurrence or progression on last systemic therapy prior to enrollment. * Progression following a non-steroidal aromatase inhibitor * Falling into one of the following categories * elderly patients (age ≥ 70 years and BMI \< 30 kg/m2); or * obese patients (BMI ≥ 30 kg/m2 and age \< 70 years); or * control patients (BMI \< 30 kg/m2 and age \< 70 years); * Serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 5 x ULN * Adequate renal function: calculated creatinine clearance, as estimated by GFR using the MDRD formula, is ≥ 30ml/min/1.73m2 * Performance status ECOG 0 - 2 (Karnofsky index: 60 - 100) * Patient is willing and able to sign the Informed Consent Form prior to screening evaluations Exclusion Criteria: * Patients aged ≥ 70 years AND BMI ≥ 30 kg/m2 * HER2-overexpressing patients by local laboratory testing (IHC 3+ staining or in situ hybridization positive). * Previous treatment with exemestane or mTOR inhibitors. Except for the treatment with exemestane in the adjuvant setting. * Known hypersensitivity to mTOR inhibitors, e.g. sirolimus (rapamycin). * Patients with a known history of HIV seropositivity. * Any severe and / or uncontrolled medical conditions such as: * Unstable angina pectoris, serious uncontrolled cardiac arrhythmia * Patients with severe hepatic impairment (Child-Pugh A/B/C) * Uncontrolled diabetes mellitus * Impairment of gastrointestinal function or gastrointestinal disease that may significantly alter the absorption of study drugs (e.g., ulcerative disease, uncontrolled nausea, vomiting, diarrhea, malabsorption syndrome) * Patients who test positive for hepatitis B or C * Patients being treated with drugs recognized as being strong inhibitors or inducers of the isoenzyme CYP3A within the last 5 days prior to enrollment * History of non-compliance to medical regimens * Patients unwilling to or unable to comply with the protocol