BackgroundThe US National Cancer Institute (NCI) has developed the Patient-Reported Outcomes version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE) to capture patients’ self-reported symptomatic adverse events in cancer clinical trials. The aim of this study was to develop and linguistically validate a Japanese translation of PRO-CTCAE. Forward- and back-translations were produced, and an independent review was performed by the Japan Clinical Oncology Group (JCOG) Executive Committee and the US NCI. We then conducted cognitive interviews with 21 patients undergoing cancer treatment. Participants were asked to complete the PRO-CTCAE and were interviewed using semi-structured scripts and predetermined probes to investigate whether any items were difficult to understand or answer. The interviews were recorded and transcribed, and a thematic analysis was performed. The data were split into two categories: 1) remarks on the items and 2) remarks on the questionnaire in general.ResultsTwenty-one cancer patients undergoing chemotherapy or hormone therapy were interviewed at the University of Tokyo Hospital and the Kansai Medical University Hirakata Hospital during 2011 and 2012. Thirty-three PRO-CTCAE items were evaluated as “difficult to understand,” and 65 items were evaluated as “difficult to answer” by at least one respondent. However, on further investigation, only 24 remarks were categorized as “comprehension difficulties” or “clarity” issues. Most of these remarks concerned patients’ difficulties with rating their experience of individual symptomatic events.ConclusionsThe study provides preliminary evidence supporting the linguistic validity of the Japanese version of PRO-CTCAE. Further cognitive interviewing is warranted for PRO-CTCAE items relating to sexuality and anxiety and for response options on severity attribute items.