A single-center retrospective analysis of the efficacy and safety of a modified regimen of irinotecan plus S-1 (IRIS) with molecular targeting agents as second-line chemotherapy in Japanese patients with recurrent or nonresectable colorectal cancer.

BACKGROUND

As the second-line chemotherapy for stage IV recurrent or nonresectable colorectal cancer, our hospital started a modified treatment regimen comprising of irinotecan plus S-1 (IRIS) [tegafur/gimeracil/oteracil (S-1)] plus molecular targeting agents (MTAs), i.e., an epidermal growth factor receptor (EGFR) inhibitor such as panitumumab (P-mab) or cetuximab (C-mab) or vascular endothelial growth factor (VEGF) inhibitor such as bevacizumab (B-mab) since October 2012. The purpose of this study is to evaluate the efficacy and safety of this modified regimen.

METHODS

This retrospective study included 41 patients with advanced recurrent colorectal cancer at our hospital whom at least 3 courses of chemotherapy were conducted from January 2015 to December 2021. Based on the location of the primary tumor, patients were classified into two group (right-sided group, proximal to the splenic curve, and left-sided, distal to the splenic curve). We assessed archived data on RAS and BRAF status and UGT1A1 polymorphisms and use of the VEGF inhibitor bevacizumab (B-mab) and the EGFR inhibitors panitumumab (P-mab) and cetuximab (C-mab). In addition, progression-free survival rate (36M-PFS) and the overall survival rate (36M-OS) were calculated. Furthermore, the respective median survival time (MST), the median number of treatment courses; the objective response rate (ORR) and clinical benefit rate (CBR) and the incidence of adverse events (AEs) were assessed as well.

RESULTS

There were 11 patients (26.8%) in the right-sided group, and 30 patients (73.2%) in the left-sided group. There were 19 patients with RAS wild type (46.3%) (1 in the right sided group and 18 in the left sided group). P-mab was used for 16 of these patients (84.2%), C-mab for 2 (10.5%), and B-mab for 1 (5.3%); the remaining 22 patients (53.7%). Ten patients in the right group and 12 patients in the left group were a mutated type and received B-mab. BRAF testing was performed in 17 patients (41.5%); as more than 50% of patients (58.5%) were included before the assay's introduction. Five patients in the right-sided group and 12 patients in the left-sided group had wild type. There was no mutated type. UGT1A1 polymorphism was tested in 16/41 patients: Eight were wild type (8/41 patients, 19.5%) and 8, mutated type. Regarding the *6/*28 double heterozygous type, there was only 1 patient in the right-sided group and the remaining 7 patients were in the left-sided group. The total number of chemotherapy courses was 299, and the median number, 6.0 (range, 3-20). PFS, OS, and MST were as follows: 36M-PFS (total/Rt/Lt), 6.2%/0.0%/8.5% (MST; 7.6/6.3/8.9 months); and 36M-OS (total/Rt/Lt), 32.1%/0.0%/44.0% (MST; 22.1/18.8/28.6 months). The ORR and CBR were 24.4% and 75.6%, respectively. The majority of AEs were grades 1 or 2 and were improved with conservative treatment. Grade 3 leukopenia was observed in 2 cases (4.9%), neutropenia in 4 cases (9.8%), and malaise/nausea/diarrhea/perforation in 1 case each (2.4%). Grade 3 leukopenia (2 patients) and neutropenia (3 patients) were more commonly observed in the left-sided group. Diarrhea and perforation were also common in the left-sided group.

CONCLUSIONS

This second-line modified IRIS regimen with MTAs is safe and effective and results in good PFS and OS.