The problem of adequate accrual is of broad concern in the medical research community and a series of reports points to certain trends:19,63

  • Fewer than one out of six cancer patients are aware of the opportunity to enroll in a clinical trial, and only 2 to 3 percent of cancer patients participate in a clinical trial.62

  • The most significant positive influences in participation are a physician’s recommendation and a relationship of trust between the physician and the patient or volunteer. However, many physicians are reluctant to encourage their patients to participate.

  • There are many reasons why people choose not to participate in clinical trials, including the demands on their time (including traveling to the study site), cumbersome processes for obtaining coverage of their medical expenses associated with participation, and a mistrust of the clinical trials process.5,19,38

  • Compared to whites, African Americans are more reluctant to participate in clinical trials, although racial and ethnic minorities representation in NCI clinical trials is comparable to their representation in the general population.44,62

  • Many participants are motivated by the desire to help others and take pride in their involvement.

However, there are different classes of clinical trials and they pose very different challenges for accrual. Trials that evaluate cancer risk or screening strategies in healthy, symptom-free people are fundamentally different from those that evaluate treatment interventions for cancer patients. The commonly perceived advantage of participating in a clinical trial—receiving the most “advanced” treatment for a life-threatening disease—does not apply to screening or detection trials. Cancer detection and screening trials generally require vast numbers of participants—as many as 20,000 to 50,000—because the endpoint (cancer incidence or death) is infrequent. For example, because roughly 5 cases of breast cancer occur per year in every 1,000 women over age 40, a study would require about 10,000 women to achieve a sample size of 50 breast cancers per year.

Cancer detection studies, such as the ongoing DMIST that is comparing digital with screen-film mammography, require thousands of subjects. But they have an advantage in that they can often be integrated into routine practice. Both recruitment of the participants and the study procedures can be conducted within existing organizations (for example, receiving regular breast screening in one’s usual health care facility). Women in the DMIST trial also receive a direct benefit from participating, which is that they receive “extra careful” screening, because they are screened with two sys-



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