Introduction
In the Nordic countries, approximately 660 children below 15 years are
diagnosed with cancer annually [1]. During the past decades,
improvements in surgical interventions, radiation and/or chemotherapy
have contributed to a major improvement in the five-year survival now
exceeding 80% for all childhood cancers combined in most high-income
countries [1]. Due to improved survival, the population of childhood
cancer survivors is steadily growing and it has been estimated that
approximately one in 1000 adults in the general population is now a
childhood cancer survivor [2].
Cancer survivors face a life with an increased risk of a wide range of
somatic and mental late effects related to their cancer diagnosis and
therapeutic exposures with a cumulative burden nearly two-fold greater
than controls [3, 4]. Several clinical studies of late effects of
childhood cancer have been conducted during the past decade. To obtain
relevant, comparable and generalisable results from the clinical
studies, the population must be representative of the survivors. Studies
with low participation might lack adequate statistical precision and
thus might be inconclusive or subject to selection bias. Factors known
to influence recruitment procedures and response rates have repeatedly
been of interest [5, 6]. Potential barriers for participation in
clinical late effect studies were analyzed in the Childhood Cancer
Survivor Study (CCSS) [4], which identified distance to the hospital
and fear of bringing back old memories of being sick as the most
important barriers. Among motivating factors were re-visiting clinicians
who had been involved in their treatment, to learn more about their own
health, and helping out other children with cancer.
Recruitment of especially adolescents and young adults (AYAs), however,
can be challenging. A study investigating recruitment of AYAs between
15-39 years in the United States through a survey achieved a response
rate of 43% [7]. Although this survey invitation was sent close to
the date of diagnosis, it required extensive resources to achieve a
sufficiently high participation rate in this age group of young people
being mobile and difficult to follow due to educational and employment
opportunities, marriage and other personal life changes.
A systematic review assessed participation reporting quality,
participation percentage and characteristics in psychosocial oncology
studies including both adult and pediatric patients [8]. Of the 156
pediatric studies included, 121 (78%) reported sufficient data to
calculate a participation rate, which was higher in studies conducted
near the time of diagnosis compared to later in the treatment
trajectory.
Willingness to participate in a clinical study seems to vary markedly
among childhood cancer survivors [9] [10], which might be due to
a variety of different factors influencing participation. However, this
has not previously been systematically investigated in childhood cancer
survivors. Thus, our aims were to outline the participation rate among
childhood cancer survivors and to investigate potential factors
influencing the participation rate, including cancer type of the
survivor, time since diagnosis, and duration of the clinical
examination. We investigated wether survivors with a cancer diagnosis
carrying a high risk of late effects such as hematologic malignancies
and central nervous system tumors, long time since diagnosis, and a long
duration of the clinical examination would lead to a lower participation
rate.