ABSTRACT
Zolbetuximab is an anti‐claudin18.2 (CLDN18.2) antibody, and the addition of zolbetuximab in combination with fluoropyrimidine and oxaliplatin as a first‐line treatment for CLDN18.2‐positive and HER2‐negative gastric or gastroesophageal junction adenocarcinoma has been shown to improve survival. However, the efficacy and safety of the combination of zolbetuximab with combinations other than fluoropyrimidine and oxaliplatin have not been elucidated. The objective of the present study is to evaluate the feasibility of combination treatment with trifluridine/tipiracil (FTD/TPI), which is effective as a third‐ or later‐line treatment, and zolbetuximab. In this study, 32 patients with CLDN18.2‐positive and HER2‐negative unresectable or recurrent gastric or gastroesophageal junction adenocarcinoma who received two or more lines of chemotherapy will be recruited. The patients will receive FTD/TPI (35 mg/m2 twice daily on days 1–5 and days 8–12 every 4 weeks) plus zolbetuximab (an initial dose of 800 mg/m2 or 400 mg/m2 depending on prior zolbetuximab exposure, followed by 400 mg/m2 every 3 weeks). The primary endpoint is treatment‐emergent events leading to the discontinuation of zolbetuximab. The secondary endpoints are the time to treatment failure, progression‐free survival, overall survival, response rate, incidence of adverse events, and incidence of Grade 3 or higher adverse events. The results will be used to evaluate the feasibility of the treatment and are expected to be used to evaluate whether future trials can be conducted.
Keywords: CLDN18.2, gastric cancer, trifluridine/tipiracil, zolbetuximab
1. Introduction
As a first‐line treatment for claudin 18.2 (CLDN18.2)‐positive and HER2‐negative unresectable advanced/recurrent gastric cancer and gastroesophageal junction adenocarcinoma, chemotherapy in combination with zolbetuximab has been shown to improve overall survival [1, 2]. In these pivotal trials, the chemotherapy used in combination with zolbetuximab was 5‐fluorouracil/leucovorin plus oxaliplatin (FOLFOX) or capecitabine plus oxaliplatin (CAPOX) [1, 2]. A certain number of cases of HER2‐negative gastric cancer and gastroesophageal junction adenocarcinoma in which first‐line treatment was already completed and in which positivity for CLDN18.2 expression is present. It is also conceivable that, on the basis of the physician's judgment, there may be cases where anti‐PD‐1 antibody drugs are prioritized over zolbetuximab in first‐line treatment, such as those with microsatellite instability‐high/deficient mismatch repair [3, 4] or high PD‐L1 expression [5]. There is no evidence supporting the use of zolbetuximab in combination with chemotherapy as second‐ or later‐line treatment for patients who were found to be CLDN18.2 positive after completing first‐line treatment or for those who did not use zolbetuximab as first‐line treatment for some reason despite being CLDN18.2 positive. Additionally, there is no information with respect to the safety and efficacy of zolbetuximab after second‐line treatment in patients who have a history of using zolbetuximab in first‐line treatment.
Trifluridine/tipiracil (FTD/TPI) is a cytotoxic anticancer drug used as a third‐ or later‐line treatment, and it has been shown to prolong overall survival compared with placebo [6]. It could be applicable to a considerable number of patients who are receiving chemotherapy after second‐line treatment. In patients who have completed first‐line and second‐line treatments, if the opportunity to use zolbetuximab can be obtained through combination therapy with FTD/TPI as third‐ or later‐line treatment, it might be expected to lead to an improvement in prognosis.
Within this context, we designed a prospective feasibility study of combination treatment of FTD/TPI with zolbetuximab as third‐ or later‐line chemotherapy for CLDN18.2‐positive and HER2‐negative gastric or gastroesophageal junction adenocarcinoma. The study will utilize fixed standard doses for both agents, and no dose escalation or de‐escalation cohorts are planned.
2. Patients and Methods
2.1. Inclusion Criteria
Patients will meet all of the following criteria:
(1) Unresectable or recurrent gastric or gastroesophageal junction adenocarcinoma.
(2) CLDN18.2‐positive and HER2‐negative status.
(3) Completed first‐line therapy, including a fluoropyrimidine‐based anticancer drug, and second‐line or subsequent therapy (with or without prior zolbetuximab administration).
(4) In patients receiving FTD/TPI, no tumor progression occurred during FTD/TPI administration.
(5) Age 18 years and older.
(6) Performance Status (PS) 0 to 1.
(7) Neutrophil count ≥ 1,500/mm3.
(8) Platelet count ≥ 75,000/mm3.
(9) Hemoglobin ≥ 8.0 g/dL (acceptable for blood transfusion).
(10) AST (GOT) ≤ 100 IU/L (≤ 200 IU/L in cases of liver metastasis).
(11) ALT (GPT) ≤ 100 IU/L (≤ 200 IU/L in cases of liver metastasis).
(12) Total bilirubin ≤ 1.5 mg/dL.
(13) Creatinine ≤ 1.5 mg/dL.
(14) Peripheral neuropathy ≤ Grade 2.
(15) Diarrhea ≤ Grade 1.
(16) Nonhematologic toxicity other than alopecia, dysgeusia, hyperpigmentation, and symptoms associated with the primary disease ≤Grade 1.
(17) No active infection.
(18) Women who may become pregnant must use appropriate contraception (oral contraceptives [progestin–estrogen combination products], intrauterine devices, or condoms for male partners) during treatment with FTD/TPI and for 6 months after the final administration of FTD/TPI.
(19) Men must use condoms for contraception during treatment with FTD/TPI and for 3 months after the final administration of FTD/TPI.
2.2. Exclusion Criteria
Patients who met any of the following criteria will be excluded from this study:
(1) Patients with tumor progression during treatment with FTD/TPI.
(2) Patients with a history of serious hypersensitivity to FTD/TPI.
(3) Patients with a history of anaphylaxis, suspected anaphylaxis, Grade 3 or higher hypersensitivity or infusion reaction, or Grade 4 vomiting, if previously treated with zolbetuximab.
(4) Patients who are pregnant, who suspect they may be pregnant, or who are breastfeeding.
2.3. Registration
Registration will be performed through REDCap of the Data Coordination Center, Department of Advanced Medicine, Nagoya University Hospital, after written informed consent is obtained.
2.4. Treatment Procedure
2.4.1. Administration of Zolbetuximab and FTD/TPI
If there is no prior history of zolbetuximab treatment, 800 mg/m2 will be administered intravenously for the first dose, and 400 mg/m2 will be administered for the second and subsequent doses at 2‐week intervals over at least 2 h. If there is a history of zolbetuximab administration, 400 mg/m2 will be administered as the first dose.
The initial dose (one dose) of FTD/TPI will be the following standard dose according to body surface area (approximately 35 mg/m2/dose as trifluridine) and will be taken twice daily after breakfast and dinner on days 1 and 8 for 5 days of each 28‐day cycle. Allow dose reduction or suspension at the discretion of the physician in charge.
Blood tests will be conducted on the day the course begins or the day before, and on the day the course starts, symptoms and physical findings will be evaluated. All of the following criteria must be met. If the criteria are not met, the start of the course will be postponed. The physician may delay the start or resumption of zolbetuximab and FTD/TPI or reduce the dosage of FTD/TPI on the basis of their judgment.
2.4.2. Criteria for Initiation and Resumption of Administration
Patients must meet all of the following criteria to start or restart the study drugs.
(1) Neutrophil count ≥ 1,500/mm3.
(2) Platelet count ≥ 75,000/mm3.
(3) Hemoglobin ≥ 8.0 g/dL (blood transfusion allowed).
(4) AST (GOT) ≤ 100 IU/L (≤ 200 IU/L if liver metastases are present).
(5) ALT (GPT) ≤ 100 IU/L (≤ 200 IU/L if liver metastases are present).
(6) Total bilirubin ≤ 1.5 mg/dL.
(7) Creatinine ≤ 1.5 mg/dL.
(8) Grade 1 or less nonhematologic toxicity other than hair loss, dysgeusia, pigmentation, and symptoms associated with the primary disease.
2.4.3. FTD/TPI Withdrawal Criteria
If any of the following criteria are met during the period of administration, FTD/TPI should be withdrawn until the above criteria for initiation and resumption are met.
(1) Neutrophil count < 1000/mm3.
(2) Platelet count < 50,000/mm3.
(3) Hemoglobin < 7.0 g/dL.
(4) AST > 100 IU/L (> 200 IU/L if liver metastases are present).
(5) ALT > 100 IU/L (> 200 IU/L if liver metastases are present).
(6) Total bilirubin > 2.0 mg/dL.
(7) Creatinine > 1.5 mg/dL.
(8) Grade 3 or higher nonhematologic toxicity other than hair loss, dysgeusia, pigmentation, and symptoms associated with the primary disease.
2.4.4. FTD/TPI Dose Reduction Criteria
If the following dose reduction criteria are met in the previous course, and if any of the adverse events listed below occurred in the previous course, the dose of FTD/TPI should be reduced to 10 mg/day units as a daily unit dose in the next course. However, the minimum dose should be 30 mg/day. If 50 mg/day is administered, 20 mg should be administered after breakfast, and 30 mg should be administered after dinner.
(1) Neutrophil count < 500/mm3.
(2) Platelet count < 50,000/mm3.
2.4.5. Criteria for the Interruption and Discontinuation of Zolbetuximab
If Grade 2 hypersensitivity or Grade 2 infusion reactions occur, the administration of zolbetuximab will be stopped until it recovers to Grade 1 or below, and the infusion rate will be reduced after recovery. For the next administration, prophylactic premedication and administration will be provided, and zolbetuximab will be administered according to the recommended infusion rate. If Grade 3 hypersensitivity, Grade 3 infusion reaction, or anaphylaxis is suspected, zolbetuximab will be discontinued.
If nausea ≥ Grade 2 or vomiting Grade 2–3 occurs, the administration of zolbetuximab will be stopped until it recovers to Grade 1 or below and resumed at a slower infusion rate after recovery. If Grade 4 vomiting occurs, zolbetuximab will be discontinued.
2.5. Endpoints
The primary endpoint was the incidence of treatment‐emergent events leading to the discontinuation of zolbetuximab during the study period. The secondary endpoints included time to treatment failure, progression‐free survival, overall survival, response rate, incidence of adverse events, and incidence of Grade 3 or higher adverse events. Exploratory endpoints, including efficacy and safety endpoints, will be analyzed for populations with and without prior zolbetuximab administration.
2.6. Statistics
The planned sample size is 32. The sample size was determined on the basis of feasibility, using data from our hospital. Since the present study is positioned as a feasibility study, no statistical hypothesis testing will be performed. For reference, during the study treatment period (from the start of treatment until 30 days after completion), the proportion of patients experiencing adverse events leading to zolbetuximab discontinuation was 51 out of 254 (20.1%, 95% CI: 15.3%–25.5%) in the GLOW trial [2] and 55 out of 279 (19.7%, 95% CI: 15.2%–24.9%) in the SPOTLIGHT trial [1]. Therefore, if the proportion of patients experiencing adverse events leading to zolbetuximab discontinuation during the treatment period in this study was approximately 15%–25% or lower, the FTD/TPI plus zolbetuximab combination therapy was considered tolerable from a safety standpoint. This study will calculate the proportion of adverse events leading to zolbetuximab discontinuation and the corresponding 95% confidence interval to evaluate whether the regimen can be adopted for subsequent clinical trial phases, such as phase II studies. For the efficacy endpoints, the time to treatment failure, progression‐free survival (PFS), and overall survival (OS) will be analyzed with the Kaplan–Meier method. The response rate will be calculated as a proportion, along with the corresponding 95% confidence interval.
2.7. Study Timeline
Following Stage 1 in‐principle acceptance (IPA), patient recruitment and data analysis are expected to be completed by December 2026 and December 2027, respectively. The submission of the finalized Stage 2 manuscript is scheduled for June 2028.
2.8. Quality Control and Outcome‐Neutral Conditions
To ensure that the primary and secondary endpoints can be tested and interpreted rigorously, the following outcome‐neutral conditions will be monitored:
Recruitment Target and Data Completeness: The study will be considered successfully executed if the planned sample size of 32 patients is reached and primary endpoint data are available for at least 90% of the enrolled participants.
Verification of Target Expression: While archival tissue is permitted, enrollment will only proceed if the archival tissue sample is confirmed to have sufficient tumor content for a valid CLDN18.2 IHC assessment by qualified local pathology review.
Protocol Adherence: The validity of the safety data will be confirmed by ensuring that 100% of the administered doses of zolbetuximab and FTD/TPI are recorded, and any deviations from the pre‐specified dosing intervals are documented.
Management of Confounding Factors: To avoid biased interpretations of treatment‐emergent adverse events, all patients will receive prophylactic antiemetic therapy according to standard guidelines. The study team will verify that these supportive measures were implemented as planned, ensuring that any high rates of discontinuation are attributable to drug toxicity rather than suboptimal supportive care.
3. Discussion
Nausea and vomiting are notable adverse events associated with zolbetuximab treatment. Although FTD/TPI generally presents a low to moderate risk of emesis, the combination of FTD/TPI with zolbetuximab may exacerbate these symptoms. Given that patients in the third‐line setting often have reduced nutritional reserve and performance status, inadequate control of nausea could lead to early treatment discontinuation. Therefore, in this study, rigorous prophylactic antiemetic therapy will be implemented according to standard guidelines, and patients will be closely monitored to manage these toxicities promptly.
To our knowledge, there have been no prior reports of FTD/TPI plus zolbetuximab combination therapy. For patients who do not receive zolbetuximab as first‐line therapy for any reason, using it in the third‐line or later setting could improve prognosis. The benefit of readministering zolbetuximab as a third‐ or later‐line treatment in patients with a history of zolbetuximab use has not been elucidated. Zolbetuximab exerts its antitumor effects primarily through antibody‐dependent cellular cytotoxicity (ADCC) and complement‐dependent cytotoxicity (CDC). Although direct evidence is lacking, experience with other targeted monoclonal antibodies suggests that continued targeting of a preserved antigen may retain clinical activity in some contexts. Therefore, rechallenge may remain effective in later lines if CLDN18.2 expression is preserved. In other cancer types, such as HER2‐positive breast cancer, the benefit of combining cytotoxic anticancer drugs with the anti‐HER2 antibody trastuzumab, even after disease progression, is recognized [7]. The benefit of combining bevacizumab with second‐line chemotherapy after first‐line chemotherapy and the antiangiogenic drug bevacizumab has also been recognized in colorectal cancer [8]. This trial is also expected to provide some indication of the importance of using zolbetuximab beyond progression.
In this study, patients with and without prior exposure to zolbetuximab will be included in a single cohort. This design was selected because the primary objective of this study is to evaluate the feasibility and safety of the combination of FTD/TPI and zolbetuximab in third‐ or later‐line use, where treatment tolerability and overall clinical burden are common concerns regardless of prior treatment. However, we acknowledge that these two populations may differ in terms of tumor biology, prior treatment selection, and mechanisms of resistance, which may influence treatment outcomes. Therefore, combining these groups may limit the interpretability of efficacy endpoints. To address this limitation, we have pre‐specified exploratory analyses stratified by prior zolbetuximab exposure for both safety and efficacy endpoints. These analyses are intended to provide hypothesis‐generating insights into potential differences between zolbetuximab‐naïve and rechallenge populations.
With respect to biomarker assessment, while re‐biopsy to confirm CLDN18.2 positivity at the time of enrollment is scientifically ideal—particularly for patients with prior exposure to zolbetuximab—it presents practical challenges in the third‐line setting because of the invasive nature of the procedure and patient condition. Therefore, this study permits enrollment on the basis of archival tissue results. This approach aligns with the eligibility criteria of pivotal phase 3 trials. However, we acknowledge that the potential for alteration or loss of CLDN18.2 expression following prior therapies is a critical limitation. Relying on archival tissue may inadvertently lead to the inclusion of patients whose tumors no longer express the target antigen. As a result, some enrolled patients may be unlikely to derive clinical benefit from zolbetuximab, and the target population may be diluted as well, potentially leading to an underestimation of the true efficacy of the combination regimen.
Another limitation of our study protocol regarding re‐treatment is the dosing schedule for patients with prior zolbetuximab exposure. From a pharmacokinetic perspective, zolbetuximab is likely eliminated from the body during the interval between first‐line and third‐line therapies, suggesting that a re‐loading dose (800 mg/m2) would be ideal to rapidly achieve therapeutic levels. However, given that patients in the third‐line setting often have a compromised general condition and nutritional status, we prioritized safety to minimize the risk of severe infusion reactions or gastrointestinal toxicity associated with high‐dose administration. Therefore, we adopted a conservative strategy of restarting at the maintenance dose (400 mg/m2). Future trials should evaluate the necessity and safety of a loading dose in this setting on the basis of the safety data from this study.
Finally, an important safety consideration in third‐line or later treatment is the high prevalence of cancer cachexia and malnutrition. Hypoalbuminemia is a clinically relevant adverse event that is associated with zolbetuximab and may affect treatment tolerability. Although a specific baseline serum albumin level is not mandated in our eligibility criteria, the strict requirement of a performance status of 0 or 1 may exclude patients with severe cachexia. We acknowledge the lack of a defined nutritional cutoff as a limitation. Thus, we will evaluate baseline nutritional status, including serum albumin levels, as an exploratory variable to assess its correlation with treatment tolerability and the feasibility of continuing zolbetuximab.
Author Contributions
Dai Shimizu: investigation, writing – review and editing. Yachiyo Kuwatsuka: data curation, writing – review and editing. Osamu Maeda: conceptualization, investigation, writing – original draft. Chie Tanaka: investigation, writing – review and editing. Fumie Kinoshita: data curation, writing – review and editing. Kazuyuki Mizuno: investigation, writing – review and editing. Shizuki Sugita: investigation, writing – review and editing. Kazuhiro Furukawa: investigation, writing – review and editing. Takashi Hirose: investigation, writing – review and editing. Kazushi Miyata: investigation, writing – review and editing. Yuichi Ando: conceptualization, supervision, writing – review and editing. Koki Nakanishi: investigation, writing – review and editing. Mitsuro Kanda: conceptualization, supervision, writing – review and editing. Masahiko Ando: data curation, writing – review and editing. Hiroki Kawashima: conceptualization, supervision, writing – review and editing.
Funding
This work was supported by Nagoya University Hospital Funding for Clinical Development.
Ethics Statement
The Nagoya University Certified Review Board approved the study protocol (No. 2024–0401), which is registered in the Japan Registry of Clinical Trials (jRCT) as jRCTs041240161 (https://jrct.mhlw.go.jp/).
Conflicts of Interest
The authors declare no conflicts of interest.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.