Evaluation of clinical validity of an S-1 dosage formula based on renal function using data of the SPIRITS and the G-SOX trials

A phase I/II trial evaluating the safety of increased-dose S- 1 with oxaliplatin and nivolumab in HER2-negative advanced gastric cancer

BACKGROUND

We developed and refined an S-1 dosage formula based on renal function, sex, and body surface area (BSA) to achieve the target area under the concentration-time curve of 5-fluorouracil in two prospective pharmacokinetic studies. The clinical validity of the refined formula (BBT formula) was evaluated using data from the two phase III trials of fist-line chemotherapy including S-1 for advanced gastric cancer, which demonstrated that overall survival and progression-free survival tended to be shorter in patients whose S-1 standard dose, based on BSA alone, was lower than that determined using the BBT formula.

METHODS

Chemo-naïve patients with HER2-negative advanced gastric or gastroesophageal junction cancer, whose standard S-1 dose is lower than that determined using the BBT formula, receive S-1 at an increased dose based on the BBT formula plus oxaliplatin (130 mg/m2) and nivolumab (360 mg/body). The primary endpoint is the incidence of dose-limiting toxicity in six patients in the phase I part and the proportion of patients requiring S-1 dose reduction in a total of 20 patients, expecting 30% and rejecting 50% with an alpha error of 0.1 and beta error of 0.2. The secondary endpoints are adverse events, relative dose intensity, response rate, disease control rate, progression-free survival, and overall survival. A correlation study is conducted to investigate the immune profiles associated with efficacy.

DISCUSSION

This phase I/II trial evaluates the safety and efficacy of S-1 at increased doses, determined by the BBT formula, in combination with oxaliplatin and nivolumab in patients with HER2-negative advanced gastric cancer, whose standard dose of S- 1 is lower than the dose recommended dose by the BBT formula.

TRIAL REGISTRATION

This study was approved by the University of Tokyo Clinical Research Review Board (URL: https://www.ut-crescent.jp/patients/chiken_jisshi/ , review number: 2022529SP) and was initiated at 19 institutions in June 2023 (registered as jRCTs031230127).

Usefulness of an S-1 dosage formula: an exploratory analysis of randomized clinical trial (JCOG1001)

BACKGROUND

The blood concentration of S-1 and adverse events are affected by renal function. Herein, an S-1 dosage formula was developed based on renal function, indicating the dose for a target blood concentration. This study aimed to explore the usefulness of the formula in adjuvant chemotherapy for gastric cancer.

METHODS

In this ad hoc analysis of the JCOG1001 trial, which evaluated the role of bursectomy for resectable gastric cancer, the recommended dose of S-1 was calculated using the following formula: 1447.8 × (14.5 + 0.301 × CLcr + 8.23 × SEX [male = 1, female = 0]) × body surface area (BSA) (mg/day). Patients were divided into three groups by comparing the initial S-1 dose determined using BSA with the dose recommended by the formula: underdose (UD), equal dose (ED), and overdose (OD).

RESULTS

Among 686 eligible patients, 58, 304, and 324 patients were classified into the UD, ED, and OD groups. The patients' characteristics in the UD/ED/OD groups were median age (53.5/64.0/67.5 years), male sex (98.3%/75.3%/58.0%), and median BMI (24.8/22.8/22.3), respectively. The planned 1-year adjuvant S-1 therapy was completed in 74.1%/73.7%/68.5%, dose reduction was required in 8.6%/21.1%/30.6%, and treatment schedule was altered in 8.6%/17.1/19.8% in the UD/ED/OD groups, resulting in the 5-year overall survival rates of 77.3%/74.3%/77.0%, respectively. The incidences of grade > 3 anemia, thrombocytopenia, diarrhea, stomatitis, and anorexia were significantly higher in the OD group than in the ED and UD groups.

CONCLUSIONS

Dose optimization using an S-1 dosage formula can potentially reduce grade ≥ 3 adverse events for overdosed patients.