Proper adjuvant therapy in patients with borderline resectable and locally advanced pancreatic cancer who had received neoadjuvant FOLFIRINOX

Background The complete resection rate of pancreatic cancer has increased because of the advent of efficacious first-line treatments for unresectable pancreatic cancer. Still, strategies regarding adjuvant therapy after neoadjuvant FOLFIRINOX treatment remain to be established. Methods Data on 144 patients with borderline resectable and locally advanced pancreatic cancer who underwent resection after neoadjuvant FOLFIRINOX between January 2013 and April 2021 were retrospectively reviewed. Results Among the study patients, 113 patients (78.5%) were diagnosed with borderline resectable pancreatic cancer and 31 patients (21.5%) were diagnosed with locally advanced pancreatic cancer. Seventy-five patients (52.1%) received radiotherapy before surgery. After radical resection, 84 patients (58.3%) received 5-fluorouracil-based adjuvant therapy and 60 patients (41.7%) received non-5-fluorouracil-based adjuvant therapy. Adjuvant therapy with 5-fluorouracil-based regimen [hazard ratio (HR), 0.43 (95% CI, 0.21–0.87); p = 0.019], preoperative assessment as locally advanced pancreatic cancer [HR, 2.87 (95% CI, 1.08–7.64); p = 0.035], positive resection margin [HR, 3.91 (95% CI, 1.71–8.94); p = 0.001], and presence of pathologic lymph node involvement [HR, 2.31 (95% CI, 1.00–5.33), p = 0.050] were associated with decreased recurrence-free survival. Adjuvant therapy with 5-fluorouracil-based regimen [HR, 0.35 (95% CI, 0.15–0.84); p = 0.018], positive resection margin [HR, 4.14 (95% CI, 1.75–9.78); p = 0.001], presence of pathologic lymph node involvement [HR, 3.36 (95% CI, 1.23–9.15); p = 0.018], poor differentiation [HR, 5.69 (95% CI, 1.76–18.36); p = 0.004], and dose reduction during adjuvant therapy [HR, 1.78 (95% CI, 1.24–24.37); p = 0.025] were associated with decreased overall survival. Conclusions The 5-fluorouracil-based adjuvant therapy seems to be the proper adjuvant therapy for patients who received neoadjuvant FOLFIRINOX for borderline resectable and locally advanced pancreatic cancer.


Introduction
Pancreatic cancer (PC) is the fourth leading cause of death from cancer in the United States (1). Surgical resection is the only potential curative method; however, resectable PC accounts for only approximately 10%-15% of total PC (2). Furthermore, the prognosis of patients who have undergone surgery is extremely poor, with a 5-year survival rate of 10% and a recurrence rate of 80% (1,3).
Neoadjuvant therapy (NAT) rather than upfront surgery is recommended for treating non-metastatic PC with improved overall survival (OS) and increased tumor-free resection margin (RM) after surgery (4)(5)(6). Among two preferred NATs, FOLFIRINOX and gemcitabine plus nab-paclitaxel (6), robust clinical trial data comparing these two regimens as NATs are still lacking, although FOLFIRINOX has shown its efficacy through several studies (7,8). The use of various regimens of adjuvant therapy (AT) following surgical resection of PC has improved OS and disease-free survival (9)(10)(11)(12); however, data were gathered from patients who underwent upfront resection rather than NAT and subsequent resection. Until now, there are no prospective data regarding optimal AT for patients undergoing surgical resection after NAT. Furthermore, data on predictive factors for tumor recurrence and OS in these patients are scarce despite their clinical importance.
This study aimed to assess the prognostic factors and identify the proper AT for those undergoing neoadjuvant FOLFIRINOX and subsequent resection.

Patient and study design
Patients diagnosed with borderline resectable (BR) or locally advanced (LA) PC and receiving neoadjuvant FOLFIRINOX at Seoul National University Hospital from January 2013 until December 2020 were included in this study. The exclusion criteria were as follows: 1) patients who failed to receive curative resection, 2) patients who had a history of other malignancy within the five most recent years, 3) patients diagnosed with metastatic PC, 4) patients lost to follow-up, 5) patients who were followed up less than 2 months after surgery, and 6) patients who had a history of pancreatic surgery for other diseases. This study protocol was approved by the institutional review board of Seoul National University Hospital (IRB No. 1711-107-901). Data of the study patients were retrospectively collected from electronic medical records. Age, Eastern Cooperative Oncology Group performance status, tumor size, lymph node (LN) status, response to NAT, initial/perioperative serum carbohydrate antigen 19-9 (CA 19-9) levels, and pathologic reports on surgical specimens were collected, and the data were analyzed.

Assessment and definition
The patient's response to anticancer therapy was evaluated according to the RECIST 1.1 criteria (13). Recurrence-free survival (RFS) was defined as the duration in months from the date of surgery to the date of recurrence or the date of the last follow-up. OS was defined from the date of diagnosis to the date of death in months or the date of last the follow-up. Survival data were gathered from the national database from the Ministry of Public Administration. The response to NAT was evaluated by the College of American Pathologists (CAP) score (14). In the CAP scoring system, the assessment of tumor response was performed through a four-step system: no viable cancer cells (grade 0), single cells or rare small groups of cancer cells (grade 1), residual cancer with evident tumor regression but more than single cells or rare small groups of cancer cells (grade 2), and extensive residual cancer with no evident tumor regression (grade 3). There were various scoring systems of tumor response after NAT in resected PC, and according to a recent systematic review, the CAP scoring system showed the lowest risk of bias with good applicability system among existing scoring systems (15). Postoperative TNM stage was defined using the American Joint Committee on Cancer Eighth guidelines (16). Assessment of the adverse events followed the National Cancer Institute Common Toxicity Criteria (version 5.0) (17).

Treatment for borderline resectable or locally advanced pancreatic cancer
Study patients were treated with the neoadjuvant FOLFIRINOX regimen that was used in the previous study (18). Each patient underwent surgery of PC after neoadjuvant FOLFIRINOX based on the decision of a multidisciplinary team. Tumor resectability was defined following the National Comprehensive Cancer Network criteria (19). BRPC and LAPC were defined on the basis of abutment or involvement of adjacent major vessels (19). Surgical extent was evaluated by consensus of the International Study Group for Pancreatic Surgery (20).

Statistical analysis
Continuous variables were provided as median values with a 95% confidence interval (95% CI), and categorical variables were provided as numbers and proportions (%). Kaplan-Meier survival analysis and log-rank test were used to compare RFS and OS between groups. Further grouped survival analysis according to pathologic response (CAP score) and AT regimen was also performed. Multivariable Cox proportional hazards analysis was conducted using variables considered to be clinically meaningful factors affecting RFS and OS. Relative hazard ratios (HRs) of recurrence and survival were analyzed with various clinical factors. Multivariable analyses predicting recurrence and survival were also conducted with statistically significant in univariable analysis or factors thought to affect clinical outcomes. Subgroup analysis for patients who underwent neoadjuvant radiotherapy in R0 resection rate, risk for recurrence or death, and pattern of tumor recurrence was conducted. Also, subgroup analysis of prognostic factors for recurrence and death by multivariable Cox proportional hazards analysis except of patients who underwent AT without FOLFIRINOX among those in the 5-fluorouracil (5-FU)-based AT group was conducted. A p value <0.05 was considered to indicate statistical significance. All statistical analyses were conducted using SPSS v.23.0 (IBM Corp., Armonk, NY, USA).

Study patients and baseline characteristics
A total of 211 patients who were diagnosed with PC were treated with FOLFIRINOX followed by surgery during the study period, and 144 patients were finally included for this study ( Figure 1). Table 1 summarizes the baseline characteristics of the study patients. There were 74 male patients (51.4%), and the median age was 64 years. One hundred forty-two patients (98.6%) showed good performance status (ECOG <2) before neoadjuvant chemotherapy. One hundred thirteen patients (78.5%) were diagnosed with BRPC, and 31 patients (21.5%) were diagnosed with LAPC. The initial CA 19-9 level at diagnosis was 349.0 U/mL [interquartile range (IQR) 25.75-1,763.5 U/mL]. The patients underwent radical resection after a median of eight cycles FIGURE 1 Flowchart of this study. , and four (2.8%) patients were T4. Also, the report of pathologic N stage data revealed 91 (63.2%) patients with N0, 48 (33.3%) with N1, and five (3.5%) with N2. The CAP scores of the surgical specimens were as follows: four (2.8%) patients had a score of 0, 41 (28.5%) patients had a score of 1, 54 (37.5%) patients had a score of 2, and 45 (31.3%) patients had a score of 3. Welldifferentiated cancer was found in 14 (9.7%) patients, moderately differentiated cancer in 110 (76.4%) patients, and poorly differentiated cancer in 16 (11.1%) patients ( Table 2).

Prognostic factors associated with recurrence-free survival and overall survival after resection
The results of relative HRs of RFS by univariable and multivariable analyses were shown in Table 3. In this multivariable model, we found that 5-FU-based AT [HR, 0.43 B A

Results of subgroup analyses
Subgroup analysis for patients who underwent neoadjuvant radiotherapy showed no differences in R0 resection rate, risk for recurrence or death, and pattern of tumor recurrence (Supplementary Table S1). Among the patients who underwent neoadjuvant radiotherapy, patients with 5-FUbased AT showed a lower risk of recurrence in comparison with patients with non-5-FU-based AT but no differences in other clinical outcomes.
Subgroup analyses of prognostic factors for recurrence and death by multivariable Cox proportional hazards analysis except of patients who underwent AT without FOLFIRINOX among those in the 5-FU-based AT group were conducted (Supplementary Table S2). AT with FOLFIRINOX and resection margin of R0 were associated with a lower risk of tumor recurrence, and AT with FOLFIRINOX, resection margin of R0, postoperative CA 19-9 normalization, and not poorly differentiated were associated with a lower risk of death.

Discussion
Over the recent years, the number of unresectable PC patients undergoing NAT and subsequent resection is expanding because of advanced clinical outcomes of chemotherapy, and FOLFIRINOX is one of the most effective options in NAT (6,7). Accordingly, proper AT for these patients is critically necessary. This study targeted this particular group of patients and concluded that AT with 5-FU is associated with a favorable survival according to the result from multivariable Cox proportional hazards analysis, along with negative RM, negative LN involvement for prolonged RFS and OS. Furthermore, preoperative assessment as BRPC was associated with prolonged RFS, and better differentiation and maintenance of standard-dose AT were associated with prolonged OS. The recurrence rate and survival outcomes in this study were in line with those of previous studies (3,(21)(22)(23)(24)(25)(26)(27). Our study showed better OS than the reported OS of the up-front surgery strategy (5), supporting that neoadjuvant FOLFIRINOX treatment seems to be a better option than up-front surgery. The R0 resection rate reported in our study was also consistent with previous meta-analysis data (8). Therefore, it is essential to suggest the reasonable criteria to determine the proper strategy of adjuvant treatment for better outcomes in patients who underwent neoadjuvant chemotherapy. Through this study, we investigated the predictive factors by closely examining a wide variety of clinical and pathologic features.
Several factors including the absence of tumor-associated LN involvement, normalized CA 19-9 level after surgery, a negative RM, and pathologic response to NAT were proposed as prognostic factors after NAT in BRPC (26,28,29). We found that AT with 5-FU, clear RM, and no pathologic LN involvement were a favorable prognostic factor for RFS and OS in our study patients. One previous study reported that AT after neoadjuvant FOLFIRINOX therapy followed by surgery was effective for the subgroup of patients with LN involvement (27). However, there was no difference in the effect of the different ATs according to LN involvement in this study. Most of the patients in AT with 5-FU groups use FOLFIRINOX, and the excellence of this regimen was shown in the same context as demonstrated in the results of the PRODIGE 24/CCTG PA6 trial (12).
AT should be performed in a patient-stratified manner including performance status and patient tolerability, as it could be ineffective in the subgroup of patients with resected PC after neoadjuvant FOLFIRINOX. As recommended by the National Comprehensive Cancer Network guidelines (19), it still seems reasonable to determine adjuvant chemotherapy based on the response to neoadjuvant chemotherapy, and the results of this study are consistent with this recommendation. However, despite the promising result from the survival analysis by groups according to pathologic response and AT with 5-FU and univariable analysis, pathologic response (CAP score 0-2) and objective response for neoadjuvant FOLFIRNOX did not maintain the effectiveness of prognosis prediction in multivariable analysis.
Although most people using FOLFIRINOX were included, it may be crucial to include 5-FU for AT according to the result of this study. Recently, a basic research with 10 patient-derived PC organoids reported results in line with the overall observations in this study that the resistance to oxaliplatin and irinotecan was developed in organoids from patients who received neoadjuvant FOLFIRINOX, but 5-FU treatment responses were similar between organoids from naive and FOLFIRNOX-treated patients (30). Gemcitabine of better tolerability may be considered an alternative AT, especially for patients with poor performance, since FOLFIRINOX treatment is associated with more severe adverse events (12). Furthermore, completion of the planned AT was proven to be an independent prognostic factor for prolonged OS (31). Considering that a 5-FUbased AT with higher toxicity can result in dropping out midway through therapy, we anticipate that a gemcitabine-based AT for nonresponders to neoadjuvant FOLFIRINOX might be a better option. Further research into subgroup selection for AT along with a structured algorithm is needed. There were several limitations. First, the study was a retrospective study conducted in a single center. Since only the patients who underwent neoadjuvant FOLFIRINOX therapy were enrolled in this study, the sample size was small. Second, we only analyzed those who completed resection and received AT, which could introduce selection bias, and this resulted in a better survival. However, we adhered to this study design for the purpose of conducting research targeting patients in need of AT most in a real clinical setting. In addition, since the majority of the non-5-FU-based AT group did not respond to the neoadjuvant FOLFIRINOX, FOLFIRINOX was not selected as an AT after surgery, and the possibility that this could lead to selection bias should be considered. However, tumor response to neoadjuvant FOLFIRINOX was not a significant predictive factor in the multivariable analysis.
In conclusion, among BRPC and LAPC patients undergoing neoadjuvant FOLFIRINOX treatment and subsequent resection, 5-FU-based AT, negative RM, negative LN, preoperative BRPC status, better differentiation, and maintenance of standard-dose AT were associated with prolonged survival outcomes.

Data availability statement
The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

Ethics statement
The studies involving human participants were reviewed and approved by Institutional Review Board of Seoul National University Hospital. Written informed consent for participation was not required for this study in accordance with the national legislation and the institutional requirements.

Author contributions
Study concept and design: JC, MK, and WP. Acquisition or interpretation of data: JC, MK, NP, and JP. Draft of manuscript: JC, MK, and WP. Critical revision of the manuscript for important intellectual content: SL, IC, JR, Y-TK, WK, HK, and J-YJ. Study supervision: WP and SL. All authors contributed to the article and approved the submitted version.