Neoadjuvant S‐1 and oxaliplatin plus bevacizumab therapy for high‐risk locally advanced rectal cancer: A prospective multicenter phase II study

Abstract Aim We report the short/mid‐term results of surgery for high‐risk locally advanced rectal cancer (LARC) after neoadjuvant chemotherapy (NAC, four courses of S‐1 + oxaliplatin+ bevacizumab) without radiotherapy with the primary aim of ypT0‐2. Methods High‐risk LARC was defined as cT4b, mesorectal fascia (MRF) ≤1 mm (MRF+), or lateral lymph node metastasis (cLLN+) on high‐resolution MRI. The planned 32 cases from April 2018 to December 2021 were all included. Results There were 10 patients at cT4b (31.2%), 26 MRF+ (81.3%), and 22 cLLN+ (68.8%). Thirteen (40.6%) underwent NAC after a colostomy for stenosis. NAC was completed in 26 (81.2%) cases. Grade 3 or higher adverse events occurred in six (18.7%). One patient developed progressive disease (3.2%). Eleven were ycT0‐3MRF‐LLN‐ (34.3%). Curative‐intent surgery was performed on 31, with sphincter‐preserving surgery in 20, abdominoperineal resection in nine, total pelvic exenteration in two, and lateral lymph node dissection in 24. Two had R1/2 resection (6.4%). A Grade 3 or higher postoperative complication rate occurred in 3.2%. Pathological complete response and ypT0‐2 rates were 12.9% and 45.1%. Three‐year disease‐free survival rates (3yDFS) for ypT0‐2 and ypT ≥3 were 81.2%, 46.6% (p = 0.061), and 3‐year local recurrence rates (3yLR) were 0%, 48.8% (p = 0.015). 3yDFS for ycT0‐3MRF‐LLN‐ and ycT4/MRF+/LLN+ were 87.5%, 48.0% (p = 0.031) and 3yLR were 0%, 42.8% (p = 0.045). Conclusion NAC yielded a clinically significant effect in about half of high‐risk LARC patients. If NAC alone is ineffective, radiotherapy should be added, even if extended surgery is intended.


| INTRODUC TI ON
Although curative resection of localized rectal cancer is achieved with the standard procedure of autonomic nerve-preserving total mesorectal excision (TME), extended surgical treatment is a strategy for high-risk locally advanced rectal cancer (LARC) that is unresectable with TME.However, it has been shown that extended surgery alone results in a high rate of recurrence, with about half of affected patients dying of cancer. 1,2Preoperative radiotherapy (RT) has been the main approach for LARC around the world, but its ineffectiveness in reducing systemic recurrence and radiation-induced late toxicity has led to the desire for the development of effective radiation-independent treatments. 3,4 this context, it has been reported that multi-agent chemotherapy and molecular-targeted agents for unresectable colorectal cancer are effective not only for metastatic disease but also for primary lesions, and that radiotherapy may be avoided in LARC. 5,6On the other hand, in past reports, the pathologic response rate (pCR) with neoadjuvant chemotherapy (NAC) alone was not high (4.3%-13.3%)for high-risk LARC, with bevacizumab contributing to a high incidence of anastomotic leakage. 5,6However, it has been shown that a high cure rate was achieved if it were reduced to an intramural lesion (ypT0-2). 7Therefore, with surgery as a prerequisite, it is considered sufficient to obtain ypT0-2 in preoperative treatment.In addition, NAC for LARC can still be considered because it is presumed to be safe if a diverting stoma is created in anastomotic cases.Thus, we conducted this study to evaluate the safety and efficacy of S-1 + ox-aliplatin+bevacizumab (SOX+Bmab) in patients with high-risk LARC based on the diagnosis from high-resolution MRI, with the goal of ypT0-2 and diverting stoma creation in all anastomotic procedures.
We report here the results of this study.

| Patients
This was a single-arm, multi-institutional, prospective phase II study evaluating the safety and efficacy of NAC followed by surgery for high-risk LARC.This study was conducted with the approval of Hirosaki University General Certified Review Board and registered with the Japan Registry of Clinical Trials (jRCTs021180023).All participating hospitals also gave their consent to conduct this study.
Written informed consent was obtained from each patient before enrollment.

| Neoadjuvant chemotherapy
S-1 was administered orally at 80 mg/m 2 /day for 14 consecutive days followed by a 7-day rest.Oxaliplatin was started intravenously on day 1, at a dose of 130 mg/m 2 /day.Bevacizumab was given intravenously also beginning on day 1, at a dose of 7.5 mg/kg/day.Twenty-one days were assumed to be one course, and chemotherapy consisted of four courses.Surgery was carried out in 8 to 12 weeks after the end of chemotherapy.Toxicity was evaluated according to CTCAE (Common Terminology Criteria for Adverse Events), version 4.0.In case of persistent Grade 2 or higher adverse events, cytotoxic drugs were reduced to 60 mg/m 2 /day for S-1 and oxaliplatin to a dose of 100 mg/m 2 /day.

| Evaluation of staging and treatment effects
Digital examination, colonoscopy, biopsy, CT, and MRI were used to evaluate local extension and metastasis of rectal cancer.
High-resolution MRI was imaged and evaluated according to the Mercury study group. 8The evaluation of MRI was unified based on the judgment of a single radiologist.The preoperative MRI assessed tumor location, tumor height, T-stage, N-stage, MRF involvement, and extramural vascular invasion (EMVI). 9Perirectal and lateral lymph node metastasis was defined as a short axis diameter ≥5 mm. 10 MRI after treatment was evaluated within 2 weeks prior to surgery and the same items as the pretreatment evaluation were reported in addition to MRI tumor regression grade (mrTRG). 11jective response of the primary tumor was assessed by longitudinal length on the basis of the Response Evaluation Criteria in Solid Tumors (RECIST), version1.1. 12

| Surgery
Surgery was scheduled 8 to 12 weeks after the end of NAC and within 2 weeks after MRI evaluation.As a general surgical approach, the inferior mesenteric artery, the left colonic artery, and the inferior mesenteric vein were dissected, followed by TME.When the lower edge of a tumor was below the peritoneal reflection (i.e., lower rectal cancer), lateral lymph node dissection (LLND) was performed bilaterally according to Japanese guidelines. 13Bilateral LLND was also scheduled if the pretreatment MRI showed metastasis in the lateral lymph nodes (LLN) regardless of tumor location.When the prostate or uterus and vagina was judged to have invasion or broad contact after the posttreatment MRI, pelvic exenteration was indicated.An ileal conduit was created by cooperating urologists.
Postoperative complications were defined according to the Clavien-Dindo classification. 14

| Pathological assessment
Specimens were opened longitudinally along the long axis of the rectum and immersed in formalin for at least 24 h.Tissue cutting was made at 5-mm intervals in the direction of the short axis of the rectum.The mesorectum was not dissected from the lesion to evaluate the radial margin.Grading of specimens was not recorded.
Pathologic complete response (pCR) was defined as no viable tumor cells being noted in the rectum, mesorectum, or harvested lymph nodes.

| Adjuvant chemotherapy
The compliance of adjuvant 5-FU + oxaliplatin therapy was as low as about 50% for rectal cancer. 15Therefore, S-1 monotherapy was selected in this study as an adjuvant chemotherapy because of its efficacy, safety, and good compliance for stage II/III rectal cancer as shown by ACTS-RC. 16S-1 was administered orally at 80 mg/m 2 /day for 14 consecutive days followed by a 7-day rest.Twenty-one days were considered one course, and chemotherapy consisted of eight courses.Adjuvant chemotherapy was not administrated if the patient refused or the doctor judged the patient unable to tolerate it due to poor postoperative condition.

| Endpoint and statistical analyses
The primary endpoint was the T down-staging rate (ypT0-2 rate).The ypT0-2 rate was reported to be 26%-33% in high-risk LARC after NAC. 5,6The expected ypT0-2 rate was set at 30% because the patients in this study were more strictly selected for LARC that was difficult to curatively resect.The number of cases was estimated to be 29 using Simon's two-stage optimal design with a threshold ypT0-2 rate of 10% with a two-sided alpha error of 0.05 and a beta error of 0.2.The planned sample size was 32, considering the small number of dropouts.Secondary endpoints were the N down-staging rate, adverse event rate during NAC, local response rate, mrTRG, surgical complications rate, R0 rate, pCR rate, local recurrence rate (LR), disease-free survival (DFS), and overall survival (OS).LR was calculated from the date of surgery to pelvic recurrence or R2 resection, DFS was calculated from the date of enrollment to disease progression or death from any cause and OS was calculated from the date of enrollment to death from any cause, using the Kaplan-Meier method.LR and DFS were compared using a log-rank test.Data were collected up to the time of evaluation after completion of postoperative adjuvant therapy for the last enrollee.A two-sided p < 0.05 was considered statistically significant, and all statistical analyses were performed with EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which was a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria). 17

| Neoadjuvant chemotherapy
Four courses of NAC were completed in 26 patients (81.2%) (Table 2).One patient did not complete the first course due to pelvic infection and progressive disease (PD).One patient had a circumferential tumor but was treated without a stoma as non-stenotic because the scope could pass and colon perforation on the oral side of tumor occurred during the second course.One patient discontinued during the second course due to peripheral neuropathy, and two patients discontinued during the third course due to oxaliplatin allergy.One patient developed edema due to proteinuria during the fourth course and was not able to complete the program.The most frequent adverse event in all grades was peripheral neuropathy at 84.4%, and the incidence of Grade 3 or higher adverse events was 18.7%.

| DISCUSS ION
In this study, we found that there were many cases of high-risk LARC that could be cured by NAC followed by surgery.Several randomized control studies have demonstrated the benefit of surgery after RT for local control, and one recent randomized control trial (RCT) showed that surgery after NAC was equivalent to surgery after RT in terms of long-term oncological outcomes. 18RT is known to cause bowel dysfunction and radiation-induced late toxicity. 4This RCT also showed that the NAC group had significantly less postoperative bowel dysfunction than the RT group. 18In this way, expectations are high for NAC followed by surgery as a treatment strategy that seeks to preserve postoperative function while maintaining local control.
Meanwhile, the significance of NAC has been examined as induction chemotherapy prior to RT.Among them, for the first time in recent years, a treatment strategy of induction chemotherapy followed by RT and surgery was reported to contribute to improved pCR and DFS compared to a strategy of RT followed by surgery and adjuvant chemotherapy. 19A study of FOLFOX+Bmab induction chemotherapy and RT followed by surgery for high-risk LARC has also reported high pCR rates and good long-term prognosis. 20Furthermore, induction chemotherapy followed by surgery and avoiding RT in good responders was verified in a tailored treatment strategy, and no local recurrence was observed in cases of significant response, suggesting that NAC is a useful treatment strategy. 21wever, problems with multiple-drug chemotherapy were also demonstrated, especially the bevacizumab-related colorectal perforation observed in this study, which is an adverse event that should not be overlooked.In this study, NAC after stoma creation was stipulated for cases of stenosis, but the ability of the scope to pass through a bulky circumferential tumor meant it was not considered stenosis, and NAC was given in such a case without stoma creation.Although this study was limited to patients under 75 years of age and excluded cases with cardiovascular comorbidities based on reports of cardiovascular toxicity with oxaliplatin, 22 some patients did not receive adequate chemotherapy due to oxaliplatin allergy or severe peripheral neuropathy, so the completion rate was not high at 81.2%.In preoperative chemotherapy studies, completion rates for CAPOX/FOLFOX+Bmab ranged from 72%-97%, 5,6,20 while completion rates for CAPOX/FOLFOX or FOLFOXIRI were 91%-97%. 19,23,24e results raised concerns about the safety of concomitant use of molecular-targeted drugs, and considering the intestinal perforation in this study, bevacizumab should not be administered when surgery is a prerequisite.
On the other hand, the additive effect of bevacizumab in prolonging survival for unresectable patients was obvious, 25 and the SOX+Bmab regimen used in this study was comparable to FOLFOX+Bmab, 26 not to mention that for SOX, higher response rates have been reported compared to CAPOX. 27Therefore, now that upfront chemotherapy for unresectable cases has become the standard, 28 the role of surgical treatment for conversion cases is important.It is known that anastomotic leakage from rectal surgery after bevacizumab administration is high, 5 but this study is significant  because it suggests that anastomotic leakage was less likely to occur if a diverting stoma was created in patients with anastomosis.
Other findings of this study include that when MRI shows a significant response to NAC, local control could be achieved with surgical treatment that avoids radiotherapy, and that cure could be almost expected.One in three patients with NAC for high-risk LARC achieved ycT0-3MRF-LLN-, with no local recurrence, and was possible for most sphincter-sparing surgery.Although nonoperative management (NOM) with additional RT for these patients is expected, as shown in this study, high-risk LARC often requires stoma creation due to stenosis, and NOM would be difficult to achieve in such patients.Furthermore, it is still not clear whether RT or surgery provides a better quality of life, as radiation alone can induce bowel and sexual dysfunction.The development of modalities that can predict successful cases of NAC or RT is necessary to ensure safe and maximized efficacy in tailored strategies that also include NOM.
There is no clear evidence whether LLND, which has been reported to be useful in Japan, 29 or RT are effective for lateral local control, but an RCT is currently being conducted and the results are awaited (NCT03587480).However, as observed in this study, bilateral LLND is sometimes not performed in cases where it is planned, and preoperative treatment is considered essential when LLND is deemed necessary.In fact, local recurrence in bilateral LLND alone in cases with cLLN+ (≥5 mm in short axis diameter) was very high at 21.4%. 30On the other hand, the completion rate of short-term RT is almost 100%, and a total neoadjuvant therapy (TNT) strategy combining RT with NAC is expected, as its oncological benefit has recently been demonstrated. 31Currently, selective LLND after TNT for patients with cLLN+ on MRI is considered a promising strategy that maximizes safety and efficacy, with lateral local recurrence reported to be as low as 3%-4%. 324][35] The pathologic LLN+ rate after NAC for cLLN+ cases in this study was 22%, but the local recurrence rate was as high as 41% even if extended surgeries were performed.Although RT may be necessary for cLLN+ cases, there were no local recurrences in MRF-and cLLN-or good responders that were ycT0-3MRF-LLN-after NAC + LLND.This suggested selective LLND after NAC may be sufficient for such cases, but the results were based on a small number of cases and await further investigation.
There are several limitations to this study.Although this is a multicenter study, the number of cases is small, and the true factor contributing to cure may not be due to NAC because it is a single-arm, non-comparative, controlled study.Since we did not evaluate postoperative bowel dysfunction in sphincter functionpreserving surgery, it is unclear whether avoidance of RT in this study actually reduced bowel dysfunction.Since most of the cT4b cases were levator ani muscles and there were no pT4b cases, it is possible that obvious urogenital invasion cases were not included.
The adjuvant S-1 monotherapy for high-risk LARC may have been inadequate in cases of poor response to NAC.TNT would be a reasonable strategy for cases of poor response to NAC because extended surgery was often inevitable and low compliance of adjuvant 5-FU + oxaliplatin therapy was expected in such cases.
Despite these limitations, this study suggests that NAC followed by surgery for high-risk LARC is a strategy worth considering as an option in future tailored treatment.

TA B L E 1
Patient characteristics at enrollment.
tion and underwent Hartmann's operation.The median distance of the anastomotic height from the anal verge was 40 (30-70) mm.Diverting stomas were created in all anastomotic cases, and stoma closure was performed in all cases except for one who did not wish to have stoma closure.Bilateral LLND was performed in 24 cases.Five cases did not undergo LLND due to colorectal perforation, patient refusal, and lower edge of the tumor above the peritoneal reflection after NAC.Two cases resulted in unilateral LLND due to technical difficulty by fibrosis after gynecologic surgery and R2 resection in the lateral region.There was only one case of a postoperative CD complication III or higher (3.2%) with anastomotic leakage.Of the 11 patients with ycT0-3MRF-LLN, 10 (91%) underwent sphinctersparing surgery.

F I G U R E 1
Kaplan-Meier analyses of disease-free survival.(A) Patients with ypT0-2 had tended to be better disease-free survival than other patients.(B) Patients with ycT0-3 and MRF-and LLN-was significantly better disease-free survival than ycT4 or MRF+ or LLN+.LLN, Lateral lymph node; MRF, Mesorectal fascia.