Discussion
In this paper, we described the methodology, participation rates, and
data availability of the DCCSS LATER 2 study. With the clinical data
collected in the LATER 2 study, we will be able to fill gaps in
knowledge that have been identified in the published recommendations of
the International Guideline Harmonization Group
(IGHG).7
The LATER 2 study collected extensive data on clinical outcomes and
questionnaires for 2,519 childhood cancer survivors, 632 siblings and
580 parents. The data collection was finished in 2020. An important
strength of our study is that we evaluated objective clinical outcomes
by diagnostic tests using blood and urine samples in combination with
functional tests, and therefore do not rely solely on self-reported
outcomes, which can be prone to recall bias. Another strength is that we
used validated questionnaires for our outcomes. Furthermore, by
including siblings for some outcomes, we will be able to compare
prevalence of outcomes and with a control group. The availability of
detailed information on childhood cancer diagnosis and treatment enables
in-depth analyses on potential risk factors for clinical outcomes.
In the LATER 2 study there is a risk of participation bias, as we found
some differences between participants and non-participants in sex, type
of cancer, and as a result also in childhood cancer treatment. This
might under- or overestimate the prevalence of health outcomes. The
consequences of these differences may vary between outcome-specific
sub-studies. Therefore, differences between the participants and
non-participants will be tested for each sub-study to evaluate specific
patterns of potential (participation) bias specific to the health
outcomes evaluated per sub-study.
The collected clinical data will be a repository for future studies.
After completion of the primary studies on the a priori-defined
clinically relevant research questions, we will combine data from
different sub-studies, e.g. metabolic syndrome and cardiac diseases and
quality of life related to medical outcomes, to answer further
questions, which may also include health outcomes ascertained using
record linkage in the LATER 1 study (e.g. benign and malignant tumors).
In the future, it will be also be possible to link clinical parameters
measured during the LATER 2 study to health outcomes that occur later.
The current study is one of the largest clinical study among childhood
cancer study and includes a large variety of clinical outcome data
collected in all types of childhood cancer survivors. As far as we are
aware, the St. Jude Lifetime Cohort study represents the only other
endeavor of this scale covering the full spectrum of childhood cancer
types in which the burden of clinical outcomes is ascertained during a
clinical visit.8 Future collaboration will be
important to improve knowledge on rare health outcomes.
In summary, in the LATER 2 study extensive information on various
clinical and (psychosocial) health outcomes has been assessed during an
outpatient clinic visit in a large group of childhood cancer survivors.
The high-quality data will provide valuable insights into risks of and
risk factors for clinical and (psychosocial) health outcomes and factors
for early recognition of (psychosocial) health outcomes in long-term
childhood cancer survivors. With this information, we will contribute to
important gaps in knowledge and finally improve the quality of life and
care for childhood cancer survivors.