Why do Experimental Cancer Treatments Fail?

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Apr 28, 2003

When Dr. Judah Folkman's new experimental cancer treatment reached the popular press, it was treated with a great deal of hype. Although heralded as a new cancer cure, Dr. Folkman himself was circumspect about it. Through experience, he knew that many drugs that looked promising in the lab failed in human treatment. In fact, follow-up clinical trials on his angiogenesis inhibitor have been disappointing. This does not mean that the drug is ineffective, just that more needs to be learned on the proper ways to use it.

Recently, research is intense on the development of targeted therapies that are designed to work on very specific types of cancers, while not harming normal tissues. These therapies were developed based on newfound knowledge on the molecular details of the cancer process. Again, a recent review article indicated that, with one exception, a large number of these experimental drugs failed in clinical trials. Why do these promising drugs fail? The following are a few reasons:

1. Lab tests are conducted under artificial conditions and the results may not apply to human treatments. In vitro studies, such as tissue cultures, are part of the discovery process to learn the molecular and cellular changes associated with cancer. The intact body is a complex stew of molecular and cellular processes and interactions that are absent from these "test tube" experiments. The next step in the drug development process is the use of laboratory animals, especially mice, to study the process in the entire body. Although the physiology of mice is quite similar to that of humans, they are used as specially bred strains in research. For example, they may be bred to be especially prone to develop cancer. In short, lab animal studies are designed to obtain preliminary information on the effect of drugs, and neither the press nor the public should jump to conclusions regarding their effectiveness in humans.

2. The design of the clinical trial may be faulty. Laboratory studies are usually show effectiveness of the drug at an early stage of cancer development, while researchers and clinicians often consider a new drug as the last attempt to control a cancer when other treatments have failed. The cancer would now be at an advanced stage and not under the conditions where laboratory studies had shown effectiveness. Often, the new drug is used as one of a number of drugs that are used concurrently or sequentially and it can be difficult to sort out effectiveness.

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