RAS status in circulating-tumor DNA after chemotherapy in RAS-mutant mCRC: The RASMEX study (JACCRO CC-17)

RAS status in tumors is a predictive factor for the efficacy of anti-epidermal growth factor receptor (EGFR) antibodies in patients with metastatic colorectal cancer (mCRC). The tumors have heterogeneity of gene profiling, and the analysis of circulating tumor DNA (ctDNA) in blood could detect the change of gene alterations in tumors that were caused by chemotherapy in mCRC. Liquid biopsy studies have shown the change of RAS status in ctDNA after chemotherapy in RAS wild-type mCRC; however, there are few evidence in RAS mutant mCRC. We therefore conducted a prospective observational study to investigate the frequency of patients with no RAS mutations in ctDNA after standard chemotherapy in mCRC with RAS mutant tumors.

The key eligibility criteria were as follows: 1) Eastern Cooperative Oncology Group performance status 0-2, 2) histologically proven unresectable mCRC, 3) RAS mutation in tumor, 4) refractory or intolerable after response to prior 1st- or 2nd-line treatment with fluoropyrimidine-containing regimen. Blood samples were collected to measure RAS gene status in ctDNA just after 1st- or 2nd-line treatment using a BEAMing digital PCR (OncoBEAM™ RAS CRC kit). The primary endpoint was the proportion of patients with no RAS mutations in ctDNA. The secondary endpoint included the mutation allele frequency (MAF) of RAS . We expected that one patient with no RAS mutations in ctDNA would be detected in 100 patients; thus, the sample size of 300 patients was set.

Of 300 patients enrolled between April 2021 and August 2022, 241 patients filled out the eligibility criteria. Patient’s characteristics were: 71.4% left-sided primary tumor, 62.2% who were enrolled after 1st-line treatment, 16.2% liver-only metastasis, 13.7% lung-only metastasis, 8.7% peritoneum-only metastasis, 3.7% lymph node-only metastasis, and 56.8% patients with metastases of multiple sites. Of 241 patients, the proportion of patients with no RAS mutations in ctDNA was 22.8% (n=55); 7.7% (3/39) in liver-only metastasis; 44.4% (4/9) in lymph node-only metastasis; 52.4% (11/21) in peritoneum-only metastasis; 57.6% (19/33) in lung-only metastasis; and 13.1% (18/137) in patients with 2 or more metastasis sites. The proportion of disappearance of KRAS exon 3/4 or NRAS exon 2/3/4 mutations in ctDNA was higher than KRAS exon 2 mutations (43.9% vs. 27.0%). Median MAF (range) of RAS mutation in ctDNA was 4.67% (0.058-50.78) in patients with multiple metastases; 6.84% (0.27-27.59) in liver-only metastasis; 1.38% (0.22-5.19) in lymph node-only metastasis; 0.39% (0.088-13.25) in peritoneum-only metastasis; 0.26% (0.099-2.14) in lung-only metastasis. In 22 (12.1%) of 182 patients with RAS mutations in ctDNA, the mutation site of RAS genes changed from that detected in archival tissue samples before chemotherapy.

Our prospective observational study revealed not the least proportion of patients with no RAS mutations in ctDNA after 1st- or 2nd-line treatment in RAS mutant mCRC. Further analysis will be performed to evaluate the efficacy of anti-EGFR antibody treatment for patients with no RAS mutation in ctDNA after standard chemotherapy.

UMIN000043442.

This study was supported by the JACCRO staff.

The authors.

Sysmex.

N. Izawa: Honoraria (self): Chugai Pharmaceutical, Taiho Pharmaceutical, Ono Pharmaceutical, MSD, Bristrol Myers Squibb. T. Ohta: Honoraria (self): Takeda Pharmaceutical, Bristol-Myers Squibb Japan, Taiho Pharmaceutical Co., Ltd.; Research grant / Funding (self): Takeda Pharmaceutical. Y. Kagawa: Speaker Bureau / Expert testimony: Lilly, Taiho, Yakult, MSD, Bayer, Daiichisankyo, Sanofi, Chugai, Ono, Takeda, Merck. H. Satake: Honoraria (self): Ono pharmaceutical co., ltd., Daiichi Sankyo Co., Ltd., Eli Lilly Japan Co., Ltd., Merck Bio Pharma Co., Ltd., MSD Co., Ltd., Bayer Co., Ltd., Bristol-Myers Squibb Co., Ltd., Chugai Pharmaceutical Co., Ltd., Sanofi Co., Ltd., Taiho Pharmaceutical Co., Ltd., Takeda Co., Ltd. Novartis Pharma and Yakult Honsha Co., Ltd.; Research grant / Funding (institution): Ono pharmaceutical co., ltd., Daiichi Sankyo, Takeda Pharmaceutical Co., Ltd., Sanofi, Taiho Pharmaceutical Co., Ltd. Asahi Kasei. W. Ichikawa: Honoraria (self): Chugai Pharma, Merck Biopharma, Bristol-Myers Squibb ; Research grant / Funding (institution): Taiho Pharma, Chugai Pharma, Daiichi Sankyo . Y. Sunakawa: Honoraria (self): Bristol-Myers Squibb, Chugai Pharm, Eli Lilly Japan; Advisory / Consultancy: Daiichi-Sankyo, Merck Biopharm, Guardant Health; Research grant / Funding (self): Chugai Pharm, Takeda, Taiho Pharm; Research grant / Funding (institution): Ono Pharm, Parexel International, PRA health science. All other authors have declared no conflicts of interest.