IRDye 800CW PEG Contrast Agent (25-60 kDa) is a non-specific imaging agent intended to exploit EPR in tumor biology.

Enhanced permeability and retention (EPR) is a common characteristic of tumor vasculature. The vascular endothelium in the tumor microenvironment is often discontinuous, allowing molecules to diffuse into the surrounding tumor tissue. In addition to EPR, the lymphatic drainage for these regions is poor. Hence, larger molecules tend to accumulate.