What role does albumin play in paclitaxel's tumor accumulation?

Albumin is important for paclitaxel tumor accumulation mainly because of the way albumin-bound paclitaxel (nab‑paclitaxel) is handled by tumors.

• Improves delivery into tumors: Tumor tissues often have leaky vasculature and poor lymphatic drainage (the “enhanced permeability and retention” effect). Albumin takes advantage of this environment so more of the drug reaches and stays in the tumor.
• Uses albumin transport pathways: Albumin in the formulation can bind albumin receptors (notably gp60/caveolae-mediated transport and SPARC—secreted protein acidic and rich in cysteine) that are commonly upregulated in many tumors. This promotes trans-endothelial transport and uptake/retention within tumor cells and tumor stroma.
• Increases intratumoral retention vs. standard formulations: Compared with conventional paclitaxel (which uses solvents like Cremophor), nab‑paclitaxel’s albumin vehicle generally leads to higher intratumoral drug concentrations, which translates to better tumor delivery and (in some settings) improved efficacy.

In short: albumin acts as a carrier that leverages tumor biology (leaky vessels, albumin transport/receptor systems, and tumor retention), resulting in greater paclitaxel accumulation in tumors.