Efficacy of liposomal irinotecan + 5-FU/LV vs. S-1 in gemcitabine-refractory metastatic pancreatic cancer: a real-world study using inverse probability of treatment weighting.

Background: S-1 monotherapy had previously been widely used as a second-line treatment for pancreatic cancer (PC) after gemcitabine-based chemotherapy mainly in Japan. Based on the results of the NAPOLI-1 trial, the recommended second-line therapy is now liposomal irinotecan plus fluorouracil/folinic acid (nal-IRI + 5-FU/LV). However, there have been no studies comparing nal-IRI + 5-FU/LV therapy with S-1 monotherapy.

Methods: The main objective of this study was to compare overall survival (OS) in patients treated with nal-IRI + 5-FU/LV and those treated with S-1 monotherapy as second-line treatments, using the inverse probability of treatment weighting (IPTW) method. This study was conducted in 31 institutions participating in Japan Oncology Network in Hepatobiliary and Pancreas. To minimize potential biases due to the retrospective design, IPTW analysis was performed with multiple imputation, and imputed IPTW-adjusted hazard ratios and corresponding 95% confidence intervals (CIs) were estimated using a Cox proportional hazards model and combined into pooled estimates.

Results: A total of 463 metastatic PC patients were enrolled in this study (257 in the S-1 monotherapy group and 206 in the nal-IRI + 5-FU/LV group). The median OS was 7.50 months (95% CI 4.18-12.69 months) in the nal-IRI + 5-FU/LV group and 5.72 months (95% CI 2.76-10.79 months) in the S-1 monotherapy group. In the IPTW-adjusted Cox proportional hazards model, nal-IRI + 5-FU/LV was associated with a significant OS benefit (pooled IPTW-adjusted hazard ratio, 0.779; 95% CI 0.399-0.941; p = 0.025).

Conclusion: These findings support the use of nal-IRI + 5-FU/LV as standard second-line treatment for PC patients after gemcitabine-based chemotherapy.