CD44 and cancer: To evaluate the targeting specificity of the CEHPNP system, the expression of CD44 on rat aHSCs, qHSCs, normal epithelial cells (clone 9 cells), CD44-positive cancer cells (MDA-MB-231 (human breast cancer cells) and A549 cells (human lung cancer cells)), and CD44-negative cells (ZR-75-1 (human breast cancer cells)) were examined by flow cytometry.