Selection and description of cancer clinical trials participants--science or happenstance?

The selection of clinical trials participants is a critical step in study design, because it affects the generalizability of recommendations made on the basis of trial results and public acceptance of medical research. The authors assessed the heterogeneity of subgroups in cancer treatment and prevention trials and the analysis of subgroups in the evaluation of trial outcomes.

The authors reviewed published reports (1990-2000) of cancer prevention and treatment trials from 11 journals. They report here on all Phase III cancer treatment and prevention trials that had at least 100 participants and were conducted among adults in the United States. A structured abstract was developed and used to extract data from the 261 published reports. Descriptive summaries of the abstracted data provided the information included in this systematic review.

Age and gender of study participants were reported in more than 90% of these trials, whereas fewer than 30% of the trials reported race or ethnicity. Gender was reported as an explicit criterion for participant selection primarily in studies of gender specific malignancies. Race and ethnicity were reported as explicit selection criteria for participant selection for five of the prevention trials and for none of the cancer treatment trials. The 105 treatment trials that reported including both men and women had 42,355 participants, and 38.6% of those participants were women. The 26 prevention trials that reported including both men and women had 73,995 participants, and 34.7% of those participants were women. Fifty-seven treatment trials reported participant ethnic diversity: There were 45,815 participants, with 10.5% African-American participants and with less than 1% Hispanic, Asian, or Native American participants. Seventeen prevention trials reported participant ethnic diversity: There were 91,741 participants, with 5.5% African-American participants, 1.7% Hispanic participants, and less than 1% Asian or Native American participants.

Cancer treatment and prevention trial reports provide scant information about participant race and ethnicity. Such studies use participant selection criteria that do not define diverse subgroups, and few subgroup analyses are conducted. Improvements in the selection, reporting, and analysis of clinical trials participants are needed.