Patient population
This retrospective analysis included data from 221 consecutive patients who received preoperative gemcitabine-based CRT (G-CRT) between 2007 and 2017 at the Osaka International Cancer Institute. All patient were classified according to the Union for International Cancer Control (UICC) 8th edition. Details of the eligibility criteria for our G-CRT protocol have been described previously [19]. In brief, all patients eligible for preoperative CRT were required to be treatment-naïve for PC and to exhibit the radiologic findings indicative of R and BR PC according to the classification of the National Comprehensive Cancer Network (version 1, 2017) with definite evidence of tumour extension beyond the confines of the pancreas (i.e., cStage 0 or cStage I cases according to the UICC 8th edition classification were not eligible) [20]. All tumours required confirmation of invasive ductal adenocarcinoma of the pancreas based on either histological or cytological examination before the initiation of preoperative CRT.
This study primarily aimed to investigate the significance of the DUPAN-II level during preoperative treatment in the context of predicting oncological outcomes and monitoring preoperative treatment efficacy. Focusing on the patients with sufficiently elevated DUPAN-II levels, we configured several cut-off values of DUPAN-II levels, i.e. 1.5, 2, 2.5, and 3 times the upper normal limit of DUPAN-II (150 U/ml); DUPAN-II > 230, 300, 380, and 450 U/ml. There was no significant difference with the prognosis among those 4 cut-off values (Fig. 1). Therefore, we adopted DUPAN-II > 230 U/ml as a significantly elevated DUPAN-II level, in which the largest number of patients (n = 73) were included among those 4 cut-off values.
Preoperative CRT
The details of preoperative G-CRT have been described previously [8, 19, 21]. In short, three-dimensional radiation or intensity-modulated radiation therapy (IMRT) was targeted to the following fields and administered at a total radiation dose of 50–60 Gy with a daily fraction of 2–2.4 Gy five times/week: the primary pancreatic tumour, celiac and superior mesenteric arteries, retroperitoneal soft tissue, and the para-aortic region. Intravenous administration of gemcitabine (1000 mg/m2) was initiated concurrently on days 1, 8, and 15 during each 4-week cycle; this procedure was repeated for three cycles, such that the preoperative CRT was completed in 3 months after initiation.
Measurement of serum CA19-9 and DUPAN-II levels
Routine laboratory tests for CA19-9 and DUPAN-II were carried out before the initiation of preoperative therapy (pre-CA19-9 and pre-DUPAN-II) and every 4 weeks thereafter. As this study aimed to investigate whether alterations in the DUPAN-II level during preoperative CRT represented the biological response of the tumours to preoperative treatment and the consequent clinical outcomes, we assessed serum DUPAN-II levels before the initiation of preoperative treatment (pre-DUPAN-II), after the completion of preoperative treatment (post-DUPAN-II), and the proportional alteration between pre- and post-DUPAN-II levels (%DUPAN-II: log [Post DUPAN-II] / log [Pre DUPAN-II] (%)) in association with the clinicopathological factors and patient survival. Serum levels of CA19-9 and DUPAN-II were measured using chemiluminescence immunoassay (CLIA) and enzyme immunoassay (EIA) methods, respectively. Serum levels ≤ 37 U/mL for CA19-9 and ≤ 150 U/mL for DUPAN-II were considered normal in this study.
In addition to CA19-9 and DUPAN-II, we evaluated post CRT neutrophil to lymphocyte ratio (NLR) as an inflammatory marker and prognostic nutrition index (PNI) as a nutritional index, which have been reported as preoperative prognostic markers [22, 23]. We set the median value of each factor as the cut-off value.
Surgical procedure and postoperative follow-up
Our surgical procedure consisted of pancreatectomy with extensive lymphatic and connective tissue clearance and postoperative liver perfusion chemotherapy. Additional information has been reported previously by our institute [8, 19]. In the case of unresectable PC after completion of preoperative CRT, further surgical treatment was avoided. Gastrointestinal and/or choledocointestinal bypass was performed if necessary in patients intraoperatively determined to have unresectable PC. Patients with unresectable PC were treated with clinically relevant chemotherapy. Cases with PC recurrence were administered various chemotherapy and/or radiation therapies based on the clinical indications.
Postoperative follow-up consisted of routine physical examination, radiographic imaging studies, and laboratory tests, including measurement of the serum levels of CA19-9 and DUPAN-II. Both chest X-ray and abdominal computed tomography (CT)/ultrasonography were performed every 3 months to carefully monitor for the presence or absence of cancer recurrence. Additional examinations, such as positron emission tomography/magnetic resonance imaging and cytological and histopathological examinations, were also available for the determination of PC recurrence when clinically indicated.
Statistical analysis
Data are expressed as means ± standard deviation. The clinicopathological parameters were compared using Fisher’s exact and χ2 tests, while continuous variables were compared using Student’s t-tests. Overall survival was calculated from the start date of preoperative therapy to the last known date of follow-up. Survival curves were computed using the Kaplan–Meier method and differences between survival curves were compared using log-rank tests. The Cox proportional hazards regression model was used to analyse the simultaneous influence of prognostic factors. Hazard ratios (HRs) estimated from the Cox analysis were reported as relative risks with corresponding 95% confidence intervals (CIs). In all analyses, P < 0.05 was considered statistically significant. Statistical analysis was performed using JMP software version 13.2 (SAS Institute Inc., Cary, NC, USA).