Methods
Design, study population and research
setting
The Swiss Childhood Cancer Survivor Study (SCCSS) is a nationwide
follow-up study of all patients registered in the Swiss Childhood Cancer
Registry (SCCR), who were diagnosed with cancer between 1976 and 2010
before the age of 21 years, and who survived at least 5 years after
diagnosis.21 The SCCR
centrally registers all children and adolescents, who are diagnosed with
leukaemia, lymphoma, central nervous system (CNS) tumours, malignant
solid tumours, or Langerhans cell histiocytosis in
Switzerland.22,23As part of the SCCSS, we sent questionnaires to adolescent survivors of
childhood cancer aged 16-19 years at study between 2007 and 2017. The
SCCSS questionnaires were developed based on the questionnaires used in
North American and British childhood cancer survivor studies to increase
international
comparability.24,25We added questions on socio-economic characteristics adapted to the
Swiss
context.26,27We asked survivors for consent to contact their siblings as comparison
group. Adolescent siblings of the same age range (16-19 years) received
the same questionnaire between 2009 and 2012 without cancer-related
questions. Ethical approval of the SCCR and the SCCSS was granted by the
Ethics Committee of the Canton of Bern (166/2014; 2021-01462).
Outcome measures – body
image
We assessed the body image of survivors and siblings with three
statements in the questionnaire: i) I am satisfied with my body
image , ii) I would like to change a few things regarding my
body , and iii) I would like to change many things regarding my
body . These questions have been previously used in healthy adolescents
in Switzerland as part of the Swiss multicentre adolescent survey on
health in 2002
(SMASH-2002).28Survivors and siblings were asked to indicate their level of agreement
with these statements on a 4-point Likert scale (0=completely agree;
1=slightly agree; 2=slightly disagree; 3=completely disagree). For
analysis purposes we reverse coded statements ii) and iii) with higher
scores indicating a more negative body image.
Socio-demographic
characteristics
For survivors and siblings, we assessed the following socio-demographic
characteristics in the questionnaire: age at study (16-17 years; 18
years; 19 years), sex, language region in Switzerland (German; French or
Italian), migration background, and whether they currently have a
boyfriend or girlfriend (no; yes). We considered survivors as having a
migration background if they were not living in Switzerland since birth,
were not Swiss citizens since birth, or have another nationality than or
in addition to the Swiss nationality.
Clinical characteristics and chronic health
conditions
We obtained the following clinical characteristics from the SCCR: age at
diagnosis (<5 years; 5-10 years; >10 years),
cancer diagnosis according to the International Classification of
Childhood Cancer - Third edition
(ICCC-3)29, treatment,
time since diagnosis (5-10 years; 10-15 years; >15 years),
and history of relapse (no; yes). For analyses, cancer diagnoses were
categorized into leukaemia (ICCC-3 Group I), lymphoma (II), CNS tumour
(III), bone tumour and soft tissue sarcoma (VIII, IX), and other tumours
(IV, V, VI, VII, X, XI, XII, and Langerhans cell histiocytosis).
Treatment modalities were coded hierarchically into surgery only,
chemotherapy (may have had surgery), radiotherapy (may have had surgery
or chemotherapy), and haematopoietic stem cell transplantation (HSCT;
may have had surgery, chemotherapy, or radiotherapy).
In the questionnaire we collected information on chronic health
conditions involving the cardiovascular, pulmonary, and endocrine
system, hearing and vision problems, and musculoskeletal, renal or
digestive, and neurological conditions. Chronic health conditions were
asked using questions from the North
American24 and
British25 Childhood
Cancer Survivor Studies. Survivors had to indicate whether they suffer
from symptoms/ diseases involving the respective body systems. Survivors
were classified as having the chronic health condition if at least one
of the corresponding symptoms/ diseases was reported. If information on
symptoms/ diseases was missing, we assumed the condition is not present
or at least not serious, as done
previously.30 We then
created a sum score based on the number of body systems affected by
chronic health conditions for each survivor.
Statistical analysis
We used descriptive statistics to describe the study population and
chi-squared tests to compare clinical characteristics between
participating and non-participating survivors. To increase the
comparability between survivors and siblings, we standardized siblings
for age at study and sex according to the distribution in survivors as
previously done.31-33We used multivariable logistic regression with being a sibling as
outcome to calculate appropriate weights. The weight for survivors was
set to 1 and all subsequent analyses were based on weighted siblings.
First, we used chi-squared tests to compare the level of agreement with
the three body image statements between survivors and weighted siblings.
We applied ordered logistic regression to identify potential differences
across ordered categories. Among survivors, we then fitted ordered
logistic regression models to identify associations between the level of
agreement with the three body image statements and socio-demographic
characteristics, clinical characteristics, and chronic health
conditions. Separate models were created for each body image statement.
We a priori decided to adjust each model for the potential
confounding factors age at study and sex based on previous
literature.34 In
addition, we separately analysed the association between body image and
growth hormone deficiency due to its relatively high prevalence and
direct impact on the
body.8 All analyses were
performed using Stata version 15.1 (StataCorp. 2017. Stata
Statistical Software: Release 15 . College Station, TX: StataCorp LLC).