This report is part of a cross-sectional study assessing functional outcomes, adverse events, psychosocial outcomes, and health-related quality of life of patients after local therapy for pediatric bone sarcoma. A detailed description of the methodology was published before [21]. In short, patients were recruited at a multidisciplinary follow-up outpatient clinic at the national Princess Máxima Center for pediatric oncology. At this outpatient clinic, patients were screened for the effects of local therapy by a team of bone sarcoma experts, consisting of a pediatric oncologist or late effects specialist, orthopedic surgeon, rehabilitation physician, physical therapist, and psychologist. The screening was conducted by history taking and a standardized measurement set, which included standardized physical examinations, adverse events reporting, and patient-reported outcome measures (PROMs). Outcomes from this multidisciplinary follow-up outpatient clinic could be used for the study if consent was obtained in accordance with the hospital’s center-wide informed consent policy, and if the patient met eligibility criteria.

The eligibility criteria for this study were as follows: (1) pediatric osteosarcoma, Ewing sarcoma, or Ewing-like sarcoma in an extremity or pelvis; (2) diagnosis of the primary tumor in or after 2003; (3) received local therapy; (4) more than 2 years after diagnosis; and (5) completed treatment without evidence of disease. Patients were excluded if they were receiving palliative care. Although individuals diagnosed within the past 5 years are generally referred to as patients, and those diagnosed 5 or more years ago as survivors, we referred to all participants in our manuscript as patients, regardless of the time since diagnosis.

The Medical Research Ethics Committee of the University Medical Centre Utrecht confirmed that the Medical Research Involving Human Subjects Act does not apply to this study (MvdL/avd/21/500354).

Sociodemographic and medical characteristics were extracted from the patients’ medical records.

Perceived physical appearance was assessed using the “Perceived physical appearance” scale from the Pediatric Quality of Life Inventory Cancer Module (PedsQL-CM-PPA) [22]. The scale consists of three items rated on a 5-point Likert scale, where 0 represents “never a problem” and 4 represents “almost always a problem”. Item scores are reversed so that the scale score ranges from 0 to 100, with higher scores indicating fewer problems. Psychometric properties are satisfactory with a Cronbach’s alpha of 0.7 in the current study [22]. The PedsQL-CM-PPA was administered to patients aged 8 years and older.

Body image concerns were assessed with the Body Image Scale (BIS) [23]. The scale consists of ten items rated on a 4-point Likert scale, where 0 represents “not at all” and 3 represents “very much”. The total score ranges from 0 to 30, with higher scores indicating more body image concerns. A score of ≥ 10 has been validated as an indicator of psychological distress in cancer patients [24]. The psychometric properties of the BIS are satisfactory, with a Cronbach’s alpha of 0.9 in the current study [25]. The BIS was administered to patients aged 16 years and older.

The emotion thermometers (ET) were used to measure distress, anxiety, depression, anger, and need for help [26, 27]. Each emotion was assessed on a 0 to 10 visual analogue scale, where 0 represents “no distress” and 10 represents “extreme distress”. Since no validated cut-off score is available for our population, we applied the commonly used cut-off of ≥ 4 [28]. Psychometric properties of the ET are satisfactory [28]. The ET were administered to patients aged 8 years and older.

Analyses were conducted separately for the total population, patients aged 8 to 15 years, and patients aged 16 years and older. The BIS questionnaire was only administered to patients aged 16 years and older. To ensure consistency in age groups, patients who completed the PedsQL-CM-PPA questionnaire were also divided into ≤ 15 years and ≥ 16 years. Descriptive statistics were used to analyze the sociodemographic and medical characteristics. To gain insight into perceived physical appearance (PedsQL-CM-PPA) and body image (BIS), descriptive analyses were conducted by tumor location (upper extremity, pelvis, and lower extremity) and surgery type for tumors around the knee (amputation, rotationplasty, and limb-sparing surgery). Descriptive statistics were used to explore the PedsQL-CM-PPA and BIS at the item level.

We assessed the impact of tumor location and surgery type for tumors around the knee on perceived physical appearance and body image by multiple linear regression analysis corrected for attained age, sex, and time since local therapy.

Pearson’s correlation coefficients were calculated to examine the relationship of perceived physical appearance (PedsQL-CM-PPA) and body image (BIS) with psychological difficulties (ET).

Standardized regression coefficients beta (β) of 0.2, 0.5, 0.8, as well as Pearson’s correlation coefficients of 0.1, 0.3, 0.5, were considered small, medium, and large, respectively [29].

Data from the study were analyzed using IBM SPSS Statistics, version 26. The level of statistical significance for all analyses was p < 0.05.