Background: To improve palliative care practice, the need for patients-reported outcome measures is increasing globally. The Integrated Palliative care Outcome Scale (IPOS) is a streamlined outcome scale developed to comprehensively evaluate patients’ distress. The goal of this study is to assess the reliability and validity of IPOS-Japanese version in cancer patients. Methods: This is a multicenter, cross-sectional observational study. We assessed the missing values, prevalence, test–retest reliability, criterion validity and known-group validity in Japanese adult cancer patients. Patients provided responses to IPOS, European Organization for Research and Treatment for Cancer Quality of Life Questionnaire-Core 30 (EORTC QLQ-C30), and Functional Assessment of Chronic Illness Therapy- Spiritual 12 (FACIT-Sp12). Our medical staff provided responses to Support Team Assessment Schedule (STAS). Results: One hundred forty-two patients were enrolled at six palliative care facilities. Missing values accounted for less than 1% of most items, with a maximum of 2.8%. The prevalence of symptoms was 17.7–88.7%. The intra-class correlation coefficient ranged from 0.522 to 0.951. The range of correlation coefficients with EORTC-QLQ-C30, FACIT-Sp12 and STAS as gold standards was 0.013 to 0.864 (absolute values). Total IPOS scores were positively correlated with Eastern Corporative Oncology Group Performance Status (P < 0.001). Conclusion: IPOS-Japanese version is a valid and reliable tool. The scale is useful in assessing physical, psychological, social and spiritual symptoms and in measuring outcomes of adult cancer patients in Japan.
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