The validation of the Italian version of the COmprehensive Score for financial Toxicity (COST)

Financial toxicity (FT) is the unintended, potential economic harm or damage of oncologic treatments that has become a medical problem with political implications. To assess FT, the COmprehensive Score for financial Toxicity (COST) questionnaire was developed. Since an Italian version is not available yet, we aimed to validate the Italian version of the COST questionnaire in a population of cancer patients during oncologic treatments or follow-up. A sample of Italian native outpatients were asked to fill the Italian version of the COST and five other self-administered questionnaires to assess quality of life, treatment-related symptoms, hope, distress, and unmet needs. Additionally, a subsample of patients was asked to retake the COST after 2–6 weeks. A single factor better represents the scale structure. Internal consistency and test–retest reliability were good. Evidence of convergent and discriminant validity was provided and criterion validity was established, showing that financial toxicity predicts the patient’s distress. Finally, known-groups validity was confirmed, testing the differences related to treatment-related expenses, sociodemographic characteristics, stage of the disease, and performance status. The current findings suggest the Italian version of the COST is a psychometrically sound scale that potentially offers an added value in assessing FT in patients with cancer.