Between September 2003 and December 2005, CanCORS obtained baseline interviews for 5,150 eligible participants with lung cancer and 4,911 participants with colorectal cancer. This interview was the primary mode of enrollment, conducted approximately 4 months after diagnosis. In 416 lung and 70 colorectal cases, permission for medical record abstraction was obtained from patients or their surrogates after interview participation was declined. The total numbers of enrolled participants were therefore 5,566 with lung cancer and 4,981 with colorectal cancer.
The ascertainment and enrollment process for the baseline interview is summarized in beginning with the number of patients identified using RCA in each cancer and ending in the number of patients enrolled. During the enrollment period, the Consortium identified 27,631 potential participants (14,327 with lung cancer, 13,304 with colorectal cancer). Of these, 21,872 were sampled from among those not known to be ineligible because of stage (i.e., noninvasive) or disease type, and the Consortium obtained physician consent to contact 21,335 of these individuals. As shown in , the overall response rates for the Consortium were 49% in lung cancer and 53% in colorectal cancer. The numbers of participants in the two cohorts correspond nearly exactly to the design goals for the study, so all the power and sample size goals of the study were met. Enrollment by PDCR site is provided in and demographic characteristics by cancer are shown in (CanCORS columns).
Ascertainment and Enrollment of CanCORS Participants and Response Rates to the Baseline Participant Survey
Total Enrollment by CanCORS Primary Data Collection and Resarch (PDCR) Site
Comparison of CanCORS Enrollees to Patients Diagnosed with Lung or Colorectal Cancer in All SEER Regions
The baseline telephone interviews were available in 4 different versions: 2,478 lung and 3,089 colorectal cancer patients participated in a full interview of approximately 1 hour; 607 lung and 713 colorectal cancer patients participated in a shorter, structured 20 minute interview because they did not feel well enough to participate in the longer interview; surrogates completed one of two versions, depending on whether the patient was alive but too ill to conduct a phone interview (506 lung and 523 colorectal cancer surrogates) or deceased (1366 lung and 380 colorectal cancer surrogates). A limited number of self-administered paper surveys (98 in total) were completed by patients who agreed to participate, but did not wish to be interviewed by telephone.
Among the participants eligible for a follow-up interview (participants who undertook the living patient baseline survey), we obtained either a participant or surrogate interview from 80% of patients with lung cancer and 82% of those with colorectal cancer. Despite the length and complexity of the interviews, item response rates were very high for items on all instruments, generally in excess of 99% and rarely as low as 95%. Of particular interest is the cohort for whom both self-reported survey data and medical record data from the chart abstraction were obtained. Medical records were abstracted for 78% of lung cancer participants with a baseline interview, and 72% of colorectal cancer patients with a baseline interview.
Taking into account the CanCORS sampling rates described above, shows the concordance between CanCORS as a whole and all SEER registry-diagnosed cases for the major categories of race/ethnicity, age and stage of disease. Comparisons of the proportion of patients with non-white race and ethnicity by age group are shown in . These analyses demonstrate that the CanCORS sample is well matched to SEER-diagnosed cases in both cancers, although the CanCORS cohort is somewhat younger (e.g., median age of 72 for colorectal cancer in SEER vs 67 in CanCORS) and has a slightly higher proportion of earlier stage patients.
Distribution of Non-White Patients by Race/Ethnicity and Age. Sample sizes refer to the CanCORS cohorts.
One factor contributing to representativeness of the CanCORS cohort may be the stability of the population throughout the enrollment process, from initial ascertainment to final enrollment. Notably the composition of the population changed only minimally as subjects were ascertained, sampled, contacted, consented and ultimately enrolled. For example, the proportion of the sample that was female changed by less than 2% throughout the enrollment process for either cancer. Other demographic and clinical characteristics exhibited similar stability (data not shown).
In addition to the national comparisons, we also investigated representativeness within specific SEER regions that corresponded to CanCORS PDCR populations. shows within-region comparisons by gender, race and age greater than 75 years for 6 CanCORS sites that enrolled patients from corresponding SEER regions. In general, the characteristics were well matched. Sites having the largest discrepancies with SEER were also the sites with smallest enrollment (e.g., Hawaii and Detroit, individual sites within the CRN) making definitive conclusions about representativeness in these sites difficult since confidence intervals associated with their estimates are wide and include the SEER rates.
Comparison of CanCORS Enrollees to Patients Diagnosed with Lung or Colorectal Cancer in Specific SEER Regions. Sample sizes refer to the CanCORS cohorts.