According to the Centers for Disease Control and Prevention, cancer is the second leading cause of death in the United States, exceeded only by heart disease. While there is no question that more research on cancer is essential for the development of more effective treatments, concerns about a particular way to study cancer—via personalized mouse models—continue to make headlines.
A recent article in Nature highlighted the limitations of these models, also called “mouse avatars,” which are generated to identify personalized treatments for cancer patients. Mouse avatars lack immune systems and are implanted with patient tumor samples obtained by biopsy or surgical resection. The purpose of generating these models is to test different cancer drugs to determine a therapeutic strategy for the cancer patient, based on the idea that treatments that work in the mouse avatar may work in the corresponding human patient.
While some researchers believed that the mouse avatar approach had the potential to become a routine part of cancer treatment, many shortcomings of mouse avatars have been revealed over the years:
- It is estimated that mouse avatars can only be made for half of the patients that want them because patient tumor cells do not always engraft in mice.
- Many patients pass away before the results of the mouse models are even available because of the time-consuming nature of generating and testing on a personalized mouse model.
- Cost is another concern. Companies which generate personalized mouse models for cancer patients charge over $10,000 for these services, which are not covered by insurance.
- The environment surrounding the tumor is different in mice than in human patients. Because the tumor microenvironment plays a significant role in how tumor cells grow and spread, this difference could substantially impact findings from the mouse model.
- Human tumors continuously evolve, and the tumor cells used to generate the mouse models may ultimately be different than the tumor in the human patient by the time treatment is administered. This means that treatments that may have looked promising in the mouse avatar may not necessarily work in the human patient.
- The fact that the mice are immunodeficient means they can’t be used to test immunotherapies.
There is no question that personalized models for cancer treatments are going to play an essential role in combatting cancer. But time is of the essence when treating cancer patients, and numerous pitfalls limit the usefulness of mouse avatars. And these shortcomings are in addition to the clear ethical concerns inherent in inflicting suffering upon another sentient being. It is clear, therefore, that more attention should be focused on in vitro assays that can generate human-relevant data in a timely fashion, and at less expense, than mouse avatars.