Study Protocol of Regorafenib Escalation for Colorectal Cancer ( RECC ) : A Phase II Multicenter Clinical Trial of the Efficacy and Safety of Regorafenib Dose Escalation Therapy as the Third or Fourth Line Therapy for Unresectable / Recurrent Colorectal Cancer

Objective : Regorafenib (BAY 73-4506) is an oral multikinase inhibitor that has been shown to inhibit various oncogenic stromal receptor tyrosine kinases and intracellular signaling kinase. The aim of the study is to confirm the safety and effectiveness of dose escalation therapy of regorafenib for the third- or fourth- treatments of patients with unresectable and recurrent colorectal cancer. Design : This study is designed as a single-arm, prospective, non-randomized, multi-centered open label phase II trial in Japan. The study regimen consists of 28-day cycles with escalated doses of regorafenib (80-160 mg/body on days 1 to 21). This study is a dose-escalation study using a starting dose of 80 mg/day during the first seven days. In case of no adverse events related to the administration after the first seven days of the starting dose, the administration dose will be increased to 120 mg/day on days 8 to 14. The administration dose will then be increased to 160 mg/day on days 15 to 21. Primary end point is progression free survival (PFS); secondary end points include time to treatment failure, response rate, overall survival, the interval between the initial of drug administration and performance status 2, the transition rate to the following line of treatment, the cumulative dose and the incidence of adverse events of grade 3 or higher, and genetic alterations ( KRAS mutation/ BRAF mutation) in circulating cell-free DNA. Conclusions : This study may contribute to determining the efficacy of the escalation of the administration dose in patients with metastatic colorectal cancer.

Introduction 5-fluorouracil (5-FU) / leucovorin (LV), irinotecan and oxaliplatin are key chemotherapy drugs for metastatic and recurrent colorectal cancer, and combination therapies (FOLFOX, FOLFIRI) have been established as the first-and second-line treatments 1) . In recent years, the usefulness of regorafenib and TAS-102 (RECOUSE test) has been demonstrated as part of the third and fourth treatments 2) 3) , and it is expected that it will improve the prognosis of many cases in the future.
Regorafenib (BAY 73-4506) is an oral multikinase inhibitor that has been shown to inhibit various oncogenic stromal receptor tyrosine kinases and intracellular signaling kinase. Since regorafenib has a low incidence of cytopenia 4) , it is advantage for patients who undergo treatment with FOLFOX or FOLFIRI for a long time and have cytopenia. However, there have been many reports of cases in which regorafenib administration cannot be continued due to side-effects, including the hand-foot syndrome and malaise 5) . Essentially, chemotherapy should be started with the prescribed dosage and the dosage decreased in intolerable cases; i.e., de-escalation. However, many patients, in particular, Japanese patients, cannot take the standard dose of regorafenib (160 mg/body) and, it is necessary to reduce the dosage in many cases. Moreover, it is difficult to continue with regorafenib at the standard dosage. In late line treatment, discontinuation of treatment can negatively affect on the prognosis. We have experienced that even 80 mg/body, half of the standard dosage, can sometimes be effective. Therefore, we developed a hypothesis that dose escalation therapy (start at a reduced dose and then increased if acceptable) can have equivalent efficacy as standard therapy.
In a Phase I trial in Japan, regorafenib was administered without undue toxicity at 160 mg/day 4) . However, the median age of the patients in the trial was 59 years (range, 34-68 years) and it was necessary to reduce the dose for 40% of the patients during the second course. Therefore, it remains to be determined whether the standard dose should be applied to patients with colorectal cancer, which develop mainly in patients above 70 years old. In addition, we have experienced that only a few cases were able to be treated with 160 mg/day regorafenib in clinical practice.
However, there have only been a few reports of dose escalation therapy of regorafenib 6) 7) . Therefore, its effectiveness and safety have not been established. The aim of the study is to confirm the safety and effectiveness of dose escalation therapy of regorafenib for the third-or fourth-treatments of patients with unresectable and recurrent colorectal cancer.

Study design
This study is designed as a single-arm, prospective, non-randomized, multi-centered open label phase II trial in Japan. Subjects who are admitted to the participating institutions will be enrolled in this study. Written informed consent will be obtained by investigators from the patient prior to any screening or inclusion procedures. This study was registered as University Hospital Medical Information Network (UMIN) 000028933 (Registered: 1 October 2017).

Sample size analysis
We referred to the CORRECT Trial 5) for calculation of the sample size. In the study, the progression free survival (PFS) was 1.9 months. With a threshold PFS of 2.0 months and an expected PFS of 3.5 months, the simulation results indicated a sample size of 50 with α = 0.05 (both sides) for a power of 80%, based on One Arm Binomial using the Southwest Oncology Group (SWOG) Statistical Tool. With an estimated dropout of 10% of the cases, a target sample size of 55 is estimated.

Figure-1 Administration schedule
This RECC study is a dose-escalation study using a starting dose of 80 mg/day during the first seven days. In case of no adverse events related to the administration after the first seven days of the starting dose, the administration dose will be increased to 120 mg/day on days 8 to 14. The administration dose will then be increased to 160 mg/day on days 15 to 21. If any adverse events satisfying the criteria for dose reduction are observed, the administration dose will be reduced by 40 mg/day. Re-dose escalation will not be attempted after dose reduction. 8. Patients with multiple primary cancers. 9. Patients undergoing treatment with corticosteroids on an ongoing basis. 10. Other patients who are considered to be unsuitable for this study by the investigator.

Treatment
The RECC study regimen consists of 28-day cycles with escalated doses of regorafenib (80-160 mg/ body on days 1 to 21) (Figure-1). We adopt a treatment schedule, in which regorafenib is administered for twenty-one consecutive days, followed by 7 days, in which the drug is not administered.
This RECC study is a dose-escalation study using a starting dose of 80 mg/day during the first seven days. In case of no adverse events related to the administration after the first seven days of the starting dose, the administration dose will be increased to 120 mg/day on days 8 to 14. The administration dose will then be increased to 160 mg/day on days 15 to 21. If any adverse events satisfying the criteria for dose reduction are observed, the administration dose will be reduced by 40 mg/day. Re-dose escalation will not be attempted after dose reduction.

The criteria for suspension and resuming of drug administration
Assessment of adverse events will be performed using the Common Terminology Criteria for Adverse Events ver.4.0 (CTCAE ver.4.0). When hand-foot syndrome, liver dysfunction or hypertension are recognized, suspension and resuming of drug administration is treated according to the criteria for suspension and resuming of drug administration (Table-1 , 2 and 3). If other kinds of adverse events reach grade 3 or higher, drug administration will be suspended until improvement equivalent to grade 2 or lower, and resumed with a 40 mg reduction of the regorafenib dose, or discontinued (when the dose is 80 mg, the study is discontinued). In addition, the attending physicians can suspend or discontinue drug administration, as necessary. When the administration dose is 80 mg/body: The administration should be immediately stopped and symptomatic treatment should be started immediately. If improvement of the adverse events is observed after interruption for seven days (Grade 0, 1), drug administration can be resumed. If the adverse events do not improve after interruption for seven days, drug administration remains discontinued.
When the administration dose is 120 or 160 mg/body: The first time: The administration dose is reduced by 40 mg/day and symptomatic treatment should be started immediately. If the adverse events do not improve, drug administration is interrupted for seven days. If the adverse events improve after interruption for seven days (Grade 0, 1), drug administration can be resumed. If the adverse events do not improve within seven days after the initial of interruption, see below.
If improvement of adverse events is not observed within seven days after the initial interruption, or the second/third time: Administration should be interrupted immediately until the adverse events are improved (Grade 0, 1). When drug administration is resumed, the administration dose is reduced by 40 mg/day. The fourth time: drug administration is discontinued.

3
The first/second time: Symptomatic treatment should be started immediately and drug administration should be interrupted for at least seven days, until the adverse events improve (Grade 0, 1). When drug administration is resumed, the administration dose is reduced by 40 mg/day. (When the administration dose is 80 mg/body, drug administration is discontinued.) The third time: drug administration is discontinued. The administration can be continued and liver function tests should be conducted frequently until the AST/ALT is < 3.0 × ULN or to the baseline values from before administration.
3 (> 5.0 × ULN, < 20.0 × ULN) The first time: The administration should be interrupted until AST/ALT returns to < 3.0 × ULN or to the baseline values from before administration. (When the administration dose is 80 mg/body, drug administration is discontinued.) When drug administration is resumed, the administration dose is reduced by 40 mg/day and liver function test should be conducted frequently for at least four weeks. Administration can be continued and an antihypertensive should also be administered. When blood pressure is uncontrollable even under treatment with the antihypertensive, the administration dose is reduced by 40 mg/day. (When the administration dose is reduced to 80 mg/body, drug administration is discontinued.)

(Symptomatic)
Drug administration is interrupted and treatment with an antihypertensive should be continued until the symptom disappears and blood pressure becomes stable. When blood pressure remains uncontrollable even under treatment with the antihypertensive after drug administration is resumed, the administration dose is reduced by 40 mg/day. (When the administration dose is reduced to 80 mg/body, drug administration is discontinued.) 3 Drug administration is interrupted and treatment with an antihypertensive should be continued until the symptom disappears and blood pressure becomes stable. When drug administration is resumed, the administration dose is reduced by 40 mg/day. When the blood pressure remains uncontrollable even under treatment with the antihypertensive after drug administration is resumed, the administration dose is reduced by 80 mg/day.

4
Drug administration is discontinued.

Translational genomic analysis
Genetic alterations (KRAS mutation and BRAF mutation) will be studied using circulating cell-free DNA, which will be obtained prior to the initiation of treatment and during treatment. The research group will study the correlations between the genetic alterations and the patient outcome or the response to treatment with regorafenib.

Statistical considerations
All patients who are treated with regorafenib will be subject to the analysis. After enrollment, ineligible patients will be excluded from this study. The response rate with 95% confidence intervals will be calculated in all eligible patients. The Kaplan-Meier method will be used to calculate progression free survival (PFS) and overall survival (OS), and univariate analyses will be performed with the log-rank test.

Study organization role of the coordinating center
The coordinating center at Nippon Medical School will be responsible for oversight and management of the conduct of this multi-center study at all collaborating intuitions. The coordinating center is designated by mutual agreement among the participating sites.

Discussion
Regorafenib is a novel oral multikinase inhibitor that has been evaluated in clinical trials 7) 8) . Although the mechanism remains unknown, it is suggested that its efficacy may result from antiangiogenic and anti-proliferative effects, mainly through RAF inhibition 9)-11) . The efficacy of regorafenib has been demonstrated in patients with metastatic colorectal cancer 5)-8) 12) . Therefore, the widespread use of regorafenib is expected in future.
Regorafenib has a main profile of adverse events that is distinct from the first or second line chemotherapies, such as FOLFOX, FOLFIRI. Therefore, regorafenib can be applied safely to patients who have previously undergone treatment with FOLFOX or FOLFIRI; however, some previous studies have demonstrated that a proportion of patients in the clinical trials was intolerant to the recommended dose of 160 mg/body 6) 13) .
Therefore, this study may contribute to determining the efficacy of the escalation of the administration dose in patients with metastatic colorectal cancer.

Ethics approval and consent to participate
The investigators confirm that this study conforms to the Ethical Guidelines for Medical and Health Research Involving Human Subjects approved by the Ministry of Health, Labour and Welfare and the Declaration of Helsinki. This study has been approved by the Institutional Review Boards of each of the participating institutes. All patients will provide written informed consent prior to enrollment.

Competing interests
None.

Funding
All treatments in this study are covered by national health insurance. The cost for translational genomic analysis is supported by the Department of Gastroenterological Surgery, Nihon Medical University. Bayer Healthcare Pharmaceutical will play no role in the study design, conduct, data collection and restoration, results analysis or interpretation of data. There are no competing interests between this company and the investigators that would require disclosure in connection with the study.