Caelyx(R) is a formulation of doxorubicin encapsulated in pegylierte liposomes. As a result of the high liposome stability, the elimination rate from plasma is significantly decreased compared with that of free doxorubicin. Following a single dose of Caelyx 50 mg/m(2) given as a 30-min infusion to patients with advanced breast cancer, the area under the curve (AUC) for plasma doxorubicin at 24 h was 67 times higher than after infusion of non-encapsulated doxorubicin at the same dose. The distribution volume of Caelyx was similar to the human blood volume, the plasma clearance was approximately 150 ml/h/m(2). In long-term studies we detected measurable doxorubicin plasma levels even at 3 weeks following administration of Caelyx. It appears that the liposomes can extravasate relatively freely through the fenestrated endothelium of the tumor vasculature. In keeping with this concept, the tissue concentrations of doxorubicin th at we found in the tumors of patients treated with Caelyx were twice that of surrounding healthy tissues. The stability of pegylated liposomes is not affected by the combined administration of the taxane docetaxel. Hypersensitivity reactions due to Caelyx(R) can be largely avoided by prolonging the infusion duration from 30 to 60 min. If Caelyx is given at intervals of 4 to 5 weeks, cutaneous toxicity (foot-hand syndrome) will also remain manageable.