Validity of the COmprehensive Score for financial Toxicity (COST) in patients with gynecologic cancer.

Objective: Financial toxicity is a financial burden of cancer care itself, which leads to worse quality of life and higher mortality and is considered an adverse effect. The COmprehensive Score for financial Toxicity (COST) tool is a patient-reported outcome measurement used to evaluate financial toxicity. We aimed to validate the internal consistency and reproducibility of the COST tool in patients with gynecologic cancer.

Methods: In this multicenter study covering the period April 2019 to July 2021, using the COST tool in Japan, patients diagnosed with ovarian, cervical, or endometrial cancer receiving systemic anti-cancer drug therapy for more than 2 months were eligible. Patients with no out-of-pocket costs for direct medical costs were excluded. The patients answered the initial test and a retest, which was completed from 2 to 14 days after the initial test. Internal consistency and reproducibility were assessed using Cronbach's alpha and intraclass correlation coefficient (ICC), respectively. Cronbach's alpha ≥0.8 indicates good internal consistency, and ICC ≥0.8 is highly reliable.

Results: A total of 112 patients (ovarian: 50, cervical: 26, endometrial: 36) responded to the initial test, and 89 patients answered the retest from 2 to 14 days after the initial test. The median patient age was 58 (range, 28-78) years. The median COST score was 19. Cronbach's alpha showed good internal consistency at 0.83 (95% CI 0.78 to 0.87). The ICC at 0.850 (95% CI 0.777 to 0.900) showed high reliability.

Conclusions: The COST tool has good internal consistency and reliable reproducibility in patients with gynecologic cancer in Japan. The COST tool quantifies financial toxicity in the insurance system, where patients have limited out-of-pocket direct medical costs. The results support the use of the COST tool in patients with gynecologic cancer.