The chick chorioallantoic membrane (CAM) as a versatile patient-derived xenograft (PDX) platform for precision medicine and preclinical research

Patient-derived xenografts (PDX) are an increasingly valuable tool in oncology, providing biologically faithful models of many different cancer types, and potential platforms for the development of precision oncology approaches. However, PDX have primarily been established in immunodeficient rodent models, with accompanying cost and efficiency constraints that pose barriers to more widespread adoption. The chicken egg chorioallantoic membrane (CAM) is an alternative in vivo PDX model. We provide here a comprehensive review of studies that grafted primary human tissue, as opposed to cell lines, onto the CAM. Twenty publications met our criteria of having inoculated patient-derived tumor tissue onto the CAM. Successful engraftment has been reported for over a dozen tumor subtypes, supporting the appropriateness of the CAM as a PDX platform. Resemblance of xenografts to the original patient tumor, increased vascularity of the CAM following engraftment, and micrometastasis into the chick mesenchyme were frequently reported. Application of standard or experimental cancer therapies to xenografts has also been undertaken, with the discovery of both synergistic drug effects and positive associations between the assay and clinical outcome. The CAM provides opportunities for RNA and DNA based sequencing of patient tumors, and the ability to efficiently (in 5-10 days) test multiple targeted therapies on fragments derived from the same tumor. While routine use of the CAM-based PDX model would benefit from a more-complete understanding of the stromal environment of CAM xenografts and interaction with the developing avian immune system, current literature supports the model's potential as an efficient, scalable precision medicine platform.