Purpose: KRAS p.G12C mutations occur in approximately 3% of metastatic colorectal cancers (mCRC). Recently, two allosteric inhibitors of KRAS p.G12C have demonstrated activity in early phase clinical trials. There are no robust studies examining the behavior of this newly targetable population., Methods: We queried the MD Anderson Cancer Center data set for patients with colorectal cancer who harbored KRAS p.G12C mutations between January 2003 and September 2019. Patients were analyzed for clinical characteristics, overall survival (OS), and progression-free survival (PFS) and compared against KRAS nonG12C. Next, we analyzed several internal and external data sets to assess immune signatures, gene expression profiles, hypermethylation, co-occurring mutations, and proteomics., Results: Among the 4,632 patients with comprehensive molecular profiling, 134 (2.9%) were found to have KRAS p.G12C mutations. An additional 53 patients with single gene sequencing were included in clinical data but excluded from prevalence analysis allowing for 187 total patients. Sixty-five patients had de novo metastatic disease and received a median of two lines of chemotherapy without surgical intervention. For the first three lines of chemotherapy, the median PFS was 6.4 months (n = 65; 95% CI, 5.0 to 7.4 months), 3.9 months (n = 47; 95% CI, 2.9 to 5.9 months), and 3.0 months (n = 21; 95% CI, 2.0 to 3.4 months), respectively. KRAS p.G12C demonstrated higher rates of basal EGFR activation compared with KRAS nonG12C. When compared with an internal cohort of KRAS nonG12C, KRAS p.G12C patients had worse OS., Conclusion: PFS is poor for patients with KRAS p.G12C metastatic colorectal cancer. OS was worse in KRAS p.G12C compared with KRAS nonG12C patients. Our data highlight the innate resistance to chemotherapy for KRAS p.G12C patients and serve as a historical comparator for future clinical trials., Competing Interests: John Paul Shen Stock and Other Ownership Interests: Agios, SNDX Van K. Morris Honoraria: Projects in Knowledge Consulting or Advisory Role: Array Biopharma, Incyte, Servier, Boehringer Ingelheim Research Funding: Bristol-Myers Squibb, Array BioPharma, EMD Serono, Boehringer Ingelheim, Immatics Arvind Dasari Consulting or Advisory Role: Ipsen, Novartis, Voluntis, Lexicon, Advanced Accelerator Applications, Hutchison MediPharma Research Funding: Novartis, Eisai, Hutchison MediPharma, Merck, Guardant Health, Ipsen Kanwal Raghav Consulting or Advisory Role: AstraZeneca, Bayer, Eisai, Daiichi Sankyo Bryan Kee Stock and Other Ownership Interests: Medtronic Shubham Pant Honoraria: 4D Pharma Consulting or Advisory Role: TYME, Xencor, Zymeworks Research Funding: Mirati Therapeutics, Lilly, RedHill Biopharma, Xencor, Five Prime Therapeutics, Novartis, Rgenix, Sanofi/Aventis, ArQule, Bristol-Myers Squibb, Onco Response, GlaxoSmithKline, Ipsen, Astellas Pharma David Fogelman Employment: Merck Stock and Other Ownership Interests: GTx Consulting or Advisory Role: Incyte Robert A. Wolff Honoraria: Modern Medicine Patents, Royalties, Other Intellectual Property: Royalties from McGraw-Hill: Editor: M.D. Anderson Manual of Medical Oncology, 3rd edition David Hong Stock and Other Ownership Interests: MolecularMatch, Presagia, OncoResponse Consulting or Advisory Role: Bayer, Guidepoint Global, GLG, Alphasights, Axiom Biotechnologies, Merrimack, Medscape, Numab, Pfizer, Seattle Genetics, Takeda, Trieza Therapeutics, WebMD, Infinity Pharmaceuticals, Amgen, Adaptimmune, Boxer Capital, EcoR1 Capital, Tavistock, Baxter, COG, Genentech, GroupH, H.C. Wainwright, Janssen, Acuta, HCW Precision, Infinity Pharmaceuticals, Prime Oncology, ST Cube, WebMD, GroupH Research Funding: Genentech, Amgen, Daiichi Sankyo, Adaptimmune, Abbvie, Bayer, Infinity Pharmaceuticals, Kite Pharma, MedImmune, Molecular Templates, Seattle Genetics, National Cancer Institute, Fate Therapeutics, Pfizer, Aldai Norte, Novartis, Numab, Turning Point Therapeutics, Verstatem, Kyowa, Lilly, Loxo, Merck, Bristol-Myers Squibb, Eisai, Genmab, Ignyta, Mirati Therapeutics, miRNA, Mologen, Takeda, AstraZeneca, Navier, VM Pharma, Erasca, Inc Travel, Accommodations, Expenses: Genmab, Society for Immunotherapy of Cancer, Bayer Schering Pharma, ASCO, AACR, miRNA, Loxo Michael J. Overman Consulting or Advisory Role: Bristol-Myers Squibb, Roche/Genentech, Gritstone Oncology, MedImmune, Novartis, Promega, Spectrum Pharmaceuticals, Array BioPharma, Janssen, Janssen, Pfizer Research Funding: Bristol-Myers Squibb, Merck, Roche, MedImmune Scott Kopetz Stock and Other Ownership Interests: MolecularMatch, Navire, Lutris Consulting or Advisory Role: Roche, Genentech, EMD Serono, Merck, Navire, Symphogen, Holy Stone Healthcare, Amgen, Novartis, Lilly, Boehringer Ingelheim, Boston Biomedical, AstraZeneca/MedImmune, Bayer Health, Pierre Fabre, EMD Serono, Redx Pharma, Ipsen, Daiichi Sankyo, Natera, HalioDx, Lutris, Jacobio, Pfizer, Repare Therapeutics, Inivata, GlaxoSmithKline, Jazz Pharmaceuticals Research Funding: Sanofi, Biocartis, Guardant Health, Array BioPharma, Genentech/Roche, EMD Serono, MedImmune, Novartis, Amgen, Lilly, Daiichi Sankyo Benny Johnson Consulting or Advisory Role: Gritstone Oncology, Incyte, Taiho Oncology Research Funding: Bristol-Myers Squibb, Syntrix No other potential conflicts of interest were reported.John Paul Shen Stock and Other Ownership Interests: Agios, SNDX Van K. Morris Honoraria: Projects in Knowledge Consulting or Advisory Role: Array Biopharma, Incyte, Servier, Boehringer Ingelheim Research Funding: Bristol-Myers Squibb, Array BioPharma, EMD Serono, Boehringer Ingelheim, Immatics Arvind Dasari Consulting or Advisory Role: Ipsen, Novartis, Voluntis, Lexicon, Advanced Accelerator Applications, Hutchison MediPharma Research Funding: Novartis, Eisai, Hutchison MediPharma, Merck, Guardant Health, Ipsen Kanwal Raghav Consulting or Advisory Role: AstraZeneca, Bayer, Eisai, Daiichi Sankyo Bryan Kee Stock and Other Ownership Interests: Medtronic Shubham Pant Honoraria: 4D Pharma Consulting or Advisory Role: TYME, Xencor, Zymeworks Research Funding: Mirati Therapeutics, Lilly, RedHill Biopharma, Xencor, Five Prime Therapeutics, Novartis, Rgenix, Sanofi/Aventis, ArQule, Bristol-Myers Squibb, Onco Response, GlaxoSmithKline, Ipsen, Astellas Pharma David Fogelman Employment: Merck Stock and Other Ownership Interests: GTx Consulting or Advisory Role: Incyte Robert A. Wolff Honoraria: Modern Medicine Patents, Royalties, Other Intellectual Property: Royalties from McGraw-Hill: Editor: M.D. Anderson Manual of Medical Oncology, 3rd edition David Hong Stock and Other Ownership Interests: MolecularMatch, Presagia, OncoResponse Consulting or Advisory Role: Bayer, Guidepoint Global, GLG, Alphasights, Axiom Biotechnologies, Merrimack, Medscape, Numab, Pfizer, Seattle Genetics, Takeda, Trieza Therapeutics, WebMD, Infinity Pharmaceuticals, Amgen, Adaptimmune, Boxer Capital, EcoR1 Capital, Tavistock, Baxter, COG, Genentech, GroupH, H.C. Wainwright, Janssen, Acuta, HCW Precision, Infinity Pharmaceuticals, Prime Oncology, ST Cube, WebMD, GroupH Research Funding: Genentech, Amgen, Daiichi Sankyo, Adaptimmune, Abbvie, Bayer, Infinity Pharmaceuticals, Kite Pharma, MedImmune, Molecular Templates, Seattle Genetics, National Cancer Institute, Fate Therapeutics, Pfizer, Aldai Norte, Novartis, Numab, Turning Point Therapeutics, Verstatem, Kyowa, Lilly, Loxo, Merck, Bristol-Myers Squibb, Eisai, Genmab, Ignyta, Mirati Therapeutics, miRNA, Mologen, Takeda, AstraZeneca, Navier, VM Pharma, Erasca, Inc Travel, Accommodations, Expenses: Genmab, Society for Immunotherapy of Cancer, Bayer Schering Pharma, ASCO, AACR, miRNA, Loxo Michael J. Overman Consulting or Advisory Role: Bristol-Myers Squibb, Roche/Genentech, Gritstone Oncology, MedImmune, Novartis, Promega, Spectrum Pharmaceuticals, Array BioPharma, Janssen, Janssen, Pfizer Research Funding: Bristol-Myers Squibb, Merck, Roche, MedImmune Scott Kopetz Stock and Other Ownership Interests: MolecularMatch, Navire, Lutris Consulting or Advisory Role: Roche, Genentech, EMD Serono, Merck, Navire, Symphogen, Holy Stone Healthcare, Amgen, Novartis, Lilly, Boehringer Ingelheim, Boston Biomedical, AstraZeneca/MedImmune, Bayer Health, Pierre Fabre, EMD Serono, Redx Pharma, Ipsen, Daiichi Sankyo, Natera, HalioDx, Lutris, Jacobio, Pfizer, Repare Therapeutics, Inivata, GlaxoSmithKline, Jazz Pharmaceuticals Research Funding: Sanofi, Biocartis, Guardant Health, Array BioPharma, Genentech/Roche, EMD Serono, MedImmune, Novartis, Amgen, Lilly, Daiichi Sankyo Benny Johnson Consulting or Advisory Role: Gritstone Oncology, Incyte, Taiho Oncology Research Funding: Bristol-Myers Squibb, Syntrix No other potential conflicts of interest were reported., (© 2021 by American Society of Clinical Oncology.)