Abstract
Due to the long circulation time of polyethylene glycol (PEG)-modified liposomes (PEG liposomes) and the leakiness of the microvasculature in solid tumors, PEG liposomes containing anticancer drugs have been shown to accumulate preferentially in tumors. This phenomenon, known as the enhanced permeability and retention (EPR) effect, has been generally observed in many types of murine solid tumors and provides a good opportunity for passive targeting of liposomal anticancer drugs to tumor tissues. However, differences in the pathophysiological characteristics of tumors may result in different therapeutic effects in EPR effect-based therapy. In this review, various factors which would affect EPR effect-based therapy are summarized and are briefly introduced in a point-by-point fashion.
