International phase IV validation study of an EORTC quality of life questionnaire for testicular cancer patients: the EORTC QLQ-TC26

BACKGROUND: Given the high cure-rate for testicular cancer (TC) and the patients’ young age, comprehensive evaluation of health-related quality of life (HRQOL) is an important consideration in this patient population. The EORTC QLQ-TC26 questionnaire module has been developed to supplement the EORTC QLQ-C30 in assessing TC-specific HRQOL in clinical trials and routine clinical practice. This international, multicentre phase IV validation study evaluated the psychometric properties of the new module. METHODS: This international, multicentre phase IV validation study enrolled testicular cancer patients from seven European countries. Patients completed the EORTC quality of life core questionnaire EORTC QLQ-C30 and the QLQ-TC26 at two consecutive time points and a debriefing questionnaire regarding the QLQ-TC26 after baseline assessment. Psychometric evaluation included examination of the hypothesized module scale structure, internal consistency and test-retest reliability, known-groups validity, responsiveness to change over time and cross-cultural acceptability. RESULTS: Data from 313 patients (mean age 38.6, SD 9.5) were analysed. All items exhibited a high completion rate with less than 2.4% missing values except for the sexuality items (up to 8.8%). The confirmatory factor analysis supported the hypothesised scale structure of the QLQ-TC26. Test-retest reliability was good for 8 of 12 scales (intraclass correlation: R t1|t2 ranged from 0.71–0.91) and four scales did not meet the acceptable criteria. Internal consistency was good for all twelve scales (Cronbach alpha = 0.79–0.90), except Communication (alpha = 0.67) and Sexual Functioning (alpha = 0.62). The module was able to distinguish clearly between patients with differing clinical status. Responsiveness to change over time was acceptable. CONCLUSION: The EORTC QLQ-TC26 is a valid, reliable and well-accepted condition-specific questionnaire, supplementing the EORTC QLQ-C30, for the assessment of testicular cancer patients’ HRQOL in clinical trials. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s12885-018-5036-8) contains supplementary material, which is available to authorized users.