Postoperative Carbohydrate Antigen 19-9 Level as a Good Indicator of Ineffective Response to the Currently Recommended S-1 Adjuvant Chemotherapy for Pancreatic Ductal Adenocarcinoma: A Single-Center, Retrospective Study.

Purpose: The intensity of adjuvant treatment for pancreatic ductal adenocarcinomas (PDACs) has not been stratified according to the risk after resection. This study was designed to identify patients with PDACs in whom the current S-1 adjuvant treatment is ineffective.

Methods: This single-center, retrospective study included patients who underwent pancreatectomy for PDACs from 2009 to 2020 at Sendai Open Hospital and were receiving S-1 adjuvant treatment. The independent risk factors for recurrence and survival were determined by using a Cox proportional hazards regression model. The effects of S-1 adjuvant treatment and detailed patterns of recurrence were evaluated in patients with high-risk factors.

Results: Overall, 118 patients with PDAC received S-1 adjuvant treatment. Postoperative nonnormalized carbohydrate antigen (CA19-9) was a predictive risk factor for recurrence (p < 0.010; hazard ratio [HR], 3.87; 95% confidence interval [CI], 2.26-6.62) and survival (p = 0.008; HR, 2.25; 95% CI, 1.24-4.11) after S-1 adjuvant treatment. In 24 patients with nonnormalized postoperative CA19-9, S-1 monotherapy was ineffective in preventing recurrence, even during the treatment period, compared with that noted in patients who did not receive adjuvant treatment. The recurrence rate during adjuvant treatment was 41.7%; in all cases, recurrence was caused by distant metastasis. The total recurrence rate was up to 95.8%, and distant recurrence was especially frequent.

Conclusions: The current S-1 adjuvant treatment regimen is ineffective for patients with postoperative nonnormalized CA19-9. The postoperative CA19-9 level may be a good indicator for further aggressive treatment. This study may lead to further discussions on intensity stratification of adjuvant treatments for PDAC.