Xenograft models, also known as heterotransplantation models, are widely used in cancer research to study the biology of tumors and test the efficacy of new cancer therapies. In a xenograft model, human cancer cells or tissues are transplanted into an animal host, typically a mouse, to create a tumor that can be studied in vivo.

Xenograft models offer several advantages over other models of cancer, including the ability to study the effects of the human tumor microenvironment on tumor growth and response to therapy. They also allow researchers to study the metastatic behavior of cancer cells and investigate the mechanisms by which cancer cells evade the immune system.

There are two main types of xenograft models: orthotopic and ectopic. In an orthotopic model, human cancer cells are transplanted into the same organ or tissue type in the animal host as the original tumor. For example, breast cancer cells may be transplanted into the mammary fat pad of a mouse to create an orthotopic model of breast cancer. Orthotopic models are considered more physiologically relevant than ectopic models, as they allow researchers to study the interactions between cancer cells and the surrounding tissue.

In an ectopic model, human cancer cells are transplanted into a site other than the original tumor site, typically under the skin or in the flank of the animal host. Ectopic models are easier to create and are often used for high-throughput drug screening assays.

Xenograft models have been used extensively in cancer drug development, with many drugs entering clinical trials based on their efficacy in these models. However, there are some limitations to the use of xenograft models in cancer research. For example, the use of immunocompromised animal hosts may not accurately reflect the immune response to tumors in humans. Additionally, the growth of human cancer cells in an animal host may alter the biological properties of the tumor, making it less representative of the original tumor.

Despite these limitations, xenograft models remain a valuable tool in cancer research and drug development. They allow researchers to study the behavior of tumors in vivo, providing important insights into the underlying mechanisms of cancer growth and response to therapy. As our understanding of the biology of tumors continues to grow, xenograft models will continue to play a critical role in the fight against cancer.