Patient eligibility
The criteria for patient eligibility were as follows: (i) cytologically or histologically confirmed NSCLC classified as either inoperable or postoperative recurrence; (ii) harboring EGFR mutations detected by peptide nucleic acid (PNA)-locked nucleic acid (LNA) PCR clamp assay or PCR-Invader assay; (iii) previously treated with both platinum-based chemotherapy and EGFR-TKIs; (iv) confirmed disease progression during EGFR-TKI treatment; (v) no treatment between EGFR-TKI therapy and initiation of the study; (vi) ≤ 2 regimens of cytotoxic agents including postoperative adjuvant chemotherapy; (vii) Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1; (viii) adequate organ functions defined as a white blood cell (WBC) count of ≥ 3,000/mm3, neutrophil count of ≥ 1,500/mm3, platelet count of ≥ 100,000/mm3, hemoglobin level of ≥ 9.0 g/dl, and aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels of ≤ 2.5 times the upper normal limit; (ix) serum bilirubin concentration of ≤ 1.5 mg/dl; (x) serum creatinine concentration of ≤ 1.2 mg/dl; (xi) measured or calculated creatinine clearance rate of ≥ 60 ml/min; (xii) partial pressure of arterial oxygen of ≥ 60 torr or a peripheral oxygen saturation of ≥ 95%; and (xiii) provided informed consent.
The main exclusion criteria were (i) obvious interstitial pneumonia on chest X-ray; (ii) active concomitant cancer; (iii) clinically significant heart disease; (iv) uncontrolled diabetes mellitus and hypertension; (v) severe infection, diarrhea, intestinal paralysis, or intestinal obstruction; (vi) massive pleural or pericardial effusion or ascites requiring drainage; (vii) symptomatic brain metastasis; (viii) previous treatment with 5-FU or irinotecan; (ix) pregnant or lactating; (x) history of drug allergy; and (xi) other clinically significant complications or judged to be inappropriate by the investigators. The study protocol was approved by the institutional ethics committee at each participating institution.
Study design and treatment
This was a multicenter, open-label, single-arm, phase II study. The primary endpoint of this study was the disease control rate (DCR) at 8 weeks after enrollment, and the secondary endpoints were PFS, overall response rate (ORR), and safety. The sample size was determined using 30% of the threshold 8-week DCR and 60% of the estimated 8-week DCR with an α error of 0.05 and a power of 0.9. Thus, the estimated minimum sample size was 23 patients. Allowing for a patient ineligibility rate of 10%, we planned to enroll 25 patients.
Based on the results of our phase I study [16], we used 70 mg/m2 irinotecan combined with 80 mg/m2 S-1. Although in the phase I study, patients received S-1 on days 1–14 and irinotecan on days 1, 8, and 15 of each 28-day cycle, the infusion could not be administered on day 15 due to side effects in some cases. Because it is customary to administer irinotecan on days 1 and 8 of each 21-day cycle for colorectal and gastric cancer, we followed the same administration schedule for irinotecan and administered S-1 twice after meals on days 1–14 of each 21-day cycle. The S-1 dose was determined according to body surface area (BSA) as follows: 80 mg/day for patients with a BSA of < 1.25 m2, 100 mg/day for those with a BSA of 1.25–1.5 m2, and 120 mg/day for those with a BSA of ≥ 1.5 m2. Irinotecan was administered at a dose of 70 mg/m2 on days 1 and 8. Treatment courses were repeated for at least four cycles every 21 days, and patients were administered more than five cycles according to the judgment of the investigators.
The starting criteria were as follows: WBC count of ≥ 3,000/mm3, neutrophil count of ≥ 1,500/mm3, platelet count of ≥ 100,000/mm3, AST and ALT levels of ≤ 2.5 times the upper normal limit, serum bilirubin concentration of ≤ 1.5 mg/dl, serum creatinine level under the upper normal limit of the institution, absence of infectious symptoms, and non-hematological toxicities of grade 1 or lower except nausea, vomiting, and general malaise. During the course of treatment, the administration of both S-1 and irinotecan was continued with the following criteria: WBC count of ≥ 2,000/mm3, neutrophil count of ≥ 1,000/mm3, platelet count of ≥ 75,000/mm3, AST and ALT levels of ≤ 2.5 times the upper normal limit, serum bilirubin concentration of ≤ 1.5 mg/dl, serum creatinine level below the upper normal limit, and grade 1 or lower non-hematological toxicities except nausea, vomiting, and general malaise. If the criteria were not satisfied, the administration was discontinued. The doses of both S-1 and irinotecan were reduced in the event of any of the following toxicities during the previous treatment cycle: WBC count of < 1,000/mm3, neutrophil count of < 500/mm3, neutrophil count of < 1,000/mm3, a body temperature of > 38°C for 72 h under the use of granulocyte colony-stimulating factor, the incidence of grade 3 or higher peripheral neuropathy, or incidence of grade 3 or higher non-hematological toxicities except nausea, vomiting, alopecia, or general malaise. During the first reduction, the S-1 dose was reduced from 120 to 100 mg/day, 100 to 80 mg/day, and 80 to 50 mg/day according to BSA, respectively, and the irinotecan dose was not reduced. During the second reduction, the S-1 dose was reduced from 100 to 80 mg/day, 80 to 50 mg/day, and 50 to 40 mg/day according to BSA, and the irinotecan dose was reduced from 70 to 60 mg/m2. Patients could undergo two reductions before discontinuing treatment.