Cancer is a leading cause of death, ranked first or second in most developed countries such as Singapore, the USA, France, Turkey, Spain, just right after cardiovascular diseases [1] [2] [3] [4] [5] . Moreover, cancer diagnosis impact Quality-of-Life (QOL) for patients, and family-caregivers. Assessing cross-cultural validation is key in medicine and social sciences as, beyond language translation issues, the way people experience emotions and needs may vary. Cultural attributes impact

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... aregiver satisfaction with care, health and quality-of-life [6-7], necessitating cross-cultural scale, and psychometric validation studies. Cancer-caregivers quality-of-life (CQOLC) is studied in such perspective here. We actually propose to validate the most widely caregiver-QOL scale, named CQOLC [2], for the first time in Spain, and to present its more common and most divergent, characteristics against already validated CQOLC scales abroad, particularly the original American scale constructed and validated in the USA by Weitzner et al. [2] . Research framework To provide optimal health care, it is important to understand the nature and effect of caregivers' social/emotional reactions [8, 9] . A lack of information, or communication [10,11], insufficient preparation [12], the demands of daily tasks, impact caregiver QOL in a manner equal to, or greater than, the impact on patients' QOL [13, 14] , justifying a caregiver-centered approach [15, 16] . The most widely used scale used for studying oncology primary caregivers QOL is the 35-items Caregivers Quality-of-Life-Index- Abstract Objective: To validate a Spanish version of the "Caregivers Quality-of-Life-Index-Cancer" (CQOLC) in Spain (named CQOLC-S). Design: The American original CQOLC was translated, then retro-translated following international standard steps, under supervision of a steering committee. Pilot interviews permitted adaptation of items. Questionnaires in Spanish hospitals (ambulatory and hospitalization). The validation process employed exploratory and confirmatory analysis, and reliability assessment. Other useful demographics were collected for future subgroups studies. Setting: Oncology department of 2 Spanish Public Hospitals (pilot n=35; valid questionnaires n=200). Participants: Adult primary caregivers of patients with all types of solid cancer, in all phases of the disease-no restriction on cancer type or family-relationship, in contrast to most previous CQOLC studies. Intervention: None. Main outcomes measures: Sociodemographic data; CQOLC-Spain psychometric properties. Results: Six factor analyses reveal a 5-factors structure, very close to but distinct from the US original scale, distinct from the Asian and other European scales (which displayed from 1 to 9 factors). Three factors were already present in the original US scale (F1-BURDEN, F2-DISRUPTIVENESS, F3-POSITIVE ADAPTATION), while 2 new factors appeared: F4-RELATIONSHIP and F5-CONCERN FOR PATIENT. Reliability index are good (alpha=0.81, good alphas for each factor), higher extracted variance ratio (59.4%) than all previous CQOLC studies. Conclusion: The CQOLC-Spain questionnaire addressing cancer-patients primary caregivers, translated from the original CQOLC, is validated and reliable. It can be incorporated in a permanent quality-of-care improvement strategy for both caregivers and patients. Methodological improvements for sampling and for CQOLC scales validations across countries are suggested, while cross-cultural comparison demonstrates the need for ongoing research: the CQOLC-S should now be tested in Latin/North-American Spanish-speaking populations.