About CARET: Follow-up

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Rationale for Study

Design

• Eligibility Criteria

• Recruitment

• Intervention

• Follow-up

• Data Collection

Primary Publications

Follow-up

Throughout the intervention phase of the trial participants were followed with routine clinic visits and phone contacts. While the intervention was being administered, participants enrolled during the pilot phase were contacted more frequently than those enrolled during the full-scale trial. These Pilot/Vanguard participants were monitored more closely for indications of toxicity related to the study vitamins, because their longer time on study meant that any toxicity related to cumulative dose would have been most likely observed in them prior to those enrolled later in the larger (Efficacy) cohort.

The intervention was stopped in January 1996, and participants were invited to return to their study centers for a "transition" visit and final blood draw. For the remainder of active post-intervention follow-up (through 2005), participants were contacted annually by phone (1997-2000) or by mailed questionnaire (2000-2005). State cancer registry and National Death Index (NDI) linkages were conducted in 2015 to extend follow-up for endpoints. Death outcome information from the NDI linkage was complete through 2013; state cancer registry data were through 2012 for WA and CA, and through 2013 for CT. A summary of contact schedules and methods follows below.

Intervention phase, Pilot studies (1985 - 1988):
Visits	Three times a year, four months after randomization and every four months thereafter
Phone contacts	Three times a year, two months after randomization and every four months thereafter
Intervention phase, Pilot/Vanguard (1989 - 1995):
Visits	Semiannually, on and six months after the anniversary dates of randomization to the pilot study
Phone contacts	Semiannually, three and nine months after the anniversary dates of randomization to the pilot study
Intervention phase, Efficacy (1989 - 1995):
Visits	Six months and 12 months after randomization, and annually thereafter on the anniversary dates of randomization
Phone contacts	Three and nine months after randomization during the first year; and semiannually thereafter, four and eight months after the anniversary dates of randomization
Post-intervention, Transition phase (1996 - 1997):
Visits	Once on the anniversary dates of randomization
Phone contacts	Semiannually, four and eight months after the anniversary dates of randomization
Post-intervention, Phone Follow-up phase (1997 - 2000):
Phone contacts	Annually on the anniversary dates of randomization
Post-intervention, Mail Follow-up phase (2000 - 2005):
Mailed questionnaire	On the anniversary dates of randomization
Post-intervention, Passive Follow-up phase (2005 - 2013):
Registry linkages	One-time linkage to the NDI and three state cancer registries: California Cancer Registry, Connecticut Tumor Registry, and Washington State Cancer Registry. Because of state regulatory restrictions, we were not able to access the cancer registries of Oregon or Maryland.