Purpose: In the CATS (Cisplatin And TS-1) randomized trial comparing cisplatin plus either docetaxel (DP arm) or TS-1 (SP arm) in lung cancer, efficacy was found to be equivalent but the global quality of life (QOL) score was higher in the SP arm. The purpose of the current study was to identify which of the adverse events (AEs) contributed to the deterioration of QOL. Methods: QOL and AE data from the CATS trial were used to quantitatively analyze the relationship between deterioration of QOL score and occurrence of AEs. Subtracted values of the QOL score from post-chemotherapy to pre-chemotherapy were fully compared between patients with or without each AE (Student’s t test, significance level = 0.001). Multivariate linear regression analysis was also performed. Analysis of variance was performed to identify whether grade of AE(s) might be significantly correlated with the deterioration of the QOL score (significance level of 0.05). Results: As expected, gastrointestinal (GI) toxicities were associated with worsening of a variety of QOL items in both trial arms, detected by both univariate and multivariate analysis (p < 0.001 and p < 0.0001, respectively). Multivariate analysis unpredictably indicated that an increase in serum bilirubin level was the only AE that was uniquely associated with worsening of physical functioning (p = 0.0002), cognitive functioning (p < 0.0001), and financial problems (p = 0.0005) in the DP arm, although not in the SP arm. GI toxicities tended to be prolonged in the SP arm. Conclusion: An increase in serum bilirubin level may contribute to the worse global QOL of subjects in the DP arm in the CATS trial. The method we used here may be a unique approach to identify unpredictable AE(s) that worsen the QOL of patients treated by chemotherapy.
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