A Study to Determine the Activity of Caelyx With Trastuzumab and Docetaxel in the Treatment of Metastatic Breast Cancer (Study P03679)

Inclusion Criteria: Patients must fulfill all the following criteria: * Females aged 18 to 70 years-old. * Willingness to participate in the study and comply with its procedures. * Documented diagnosis of metastatic breast carcinoma (stage IV) Human Epidermal Growth Factor Receptor 2 (HER2) overexpressing (Immunohistochemistry (IHC) 3+ or Fluorescence In Situ Hybridization(FISH) +). * No prior chemotherapy for metastatic breast cancer. * Adjuvant or neo-adjuvant chemotherapy is allowed according to the following rules: * patients treated with anthracyclines if all the following conditions are met: * Doxorubicin total dose \<= 300 mg/m\^2 * Epirubicin total dose \<= 480 mg/m\^2 * Chemotherapy-free interval of \> 12 months * no taxane-based adjuvant or neo-adjuvant chemotherapy is allowed; * patients treated with non-anthracycline/taxane adjuvant or neo-adjuvant chemotherapy regimens are freely eligible (i.e. cyclophosphamide/methotrexate/fluorouracil (CMF) or similar regimens). * At least one measurable lesion according to RECIST criteria. * Complete hematologic and biologic baseline evaluation within 2 weeks prior to start of treatment. * Complete Tumor baseline evaluation including a total body computed tomography (CT) scan within 4 weeks prior to start of treatment. * Left ventricular ejection fraction (LVEF) \>= 50% as determined by echocardiogram or Multi Gated Acquisition (MUGA) scan. * World Health Organization (WHO) performance status 0,1. * Life expectancy \> 3 months. * Laboratory requirements : * Hematology : * Neutrophils \> 1.5 x 10\^9/L * Platelets \> 100 x 10\^9/L * Hemoglobin \> 10 g/dL * Hepatic function: * Total bilirubin \<= 1.25 x the upper-normal limits (UNL); * ASAT (Aspartate Aminotransferase or SGOT), ALAT (Alanine aminotransferase or SGPT) \<= 2.5 x the upper-normal limits; * For patients with liver metastases: * Total bilirubin \< 1.5 x the UNL (Upper limit of normal) ; * ASAT and/or ALAT \< 3 x the UNL; * Renal function : * Serum Creatinine \< 1.5 x the UNL. * Women of child bearing potential must have a negative serum pregnancy test and be using adequate contraception. * Patients must be accessible for treatment and follow-up. Exclusion Criteria: Patients will not be enrolled if any of the following criteria apply: * Prior chemotherapy for metastatic disease. * History of prior malignancy in the last 10 years (other than non melanoma skin cancer or excised cervical carcinoma in situ). * Radiation to disease areas within 3 weeks of study initiation. * Symptomatic peripheral neuropathy \> grade 2 according to the National Cancer Institute (NCI) Common Toxicity Criteria. * Other serious illness or medical condition. * LVEF \< 50% as determined by echocardiogram or MUGA scan. * Congestive hearth failure or angina pectoris even if it is medically controlled. Previous history of myocardial infarction within 1 year from study entry, uncontrolled high risk hypertension or arrhythmia. * History of significant neurologic or psychiatric disorders including dementia or seizures. * Active infection. * Active peptic ulcer, unstable diabetes mellitus or other contraindications for the use of dexamethasone. * Concurrent treatment with other experimental drugs. Participation in another clinical trial with any investigational drug within 30 days prior to study screening. * Concurrent treatment with corticosteroids used for reasons other than for premedication. However patients receiving chronic treatment with corticosteroids (\> 6 months) at low dose (\< 20 mg of methylprednisolone or equivalent dose of other corticosteroids) for whichever reason are eligible. * Taxane-based adjuvant or neo-adjuvant chemotherapy \< 12 months. * Other concurrent chemotherapy, immunotherapy, radiotherapy or any other investigational medication, for the treatment of the tumor. * Pregnant or breast-feeding women.