Biomarker Testing and Molecular Subtyping in First-Line mCRC

Welcome back to another AJMC Peer Exchange series. In this episode, “Biomarker Testing and Molecular Subtyping in First-Line mCRC,” the panel examines how molecular testing and patient characteristics inform first-line treatment decisions in metastatic colorectal cancer.

Patient lifestyle can also affect treatment selection. Dr. Parseghian gives the example of avoiding an oxaliplatin-containing regimen in a patient for whom neuropathy could significantly interfere with daily activities. The discussion then turns to maintenance therapy after an initial period of combination treatment. Dr. Parseghian describes transitioning patients with responding or stable disease to a less intensive regimen while discontinuing oxaliplatin or irinotecan. The maintenance strategy varies according to molecular subtype and the targeted therapy being used. The episode illustrates how first-line treatment planning must account for both initial disease control and how therapy can be adapted over time to limit cumulative toxicity and preserve future options.

The next episode in this series, “Immunotherapy in MSI-High and dMMR mCRC,” examines how immunotherapy has changed treatment for this biologically distinct patient population.

Dr. Fakih discusses the importance of establishing treatment goals and obtaining an early molecular profile before selecting systemic therapy. He describes using liquid biopsy to obtain rapid molecular information while ordering tissue-based next-generation sequencing in parallel. MSI status is a particular priority because identifying MSI-high disease can substantially alter the treatment approach. The discussion also addresses testing for RAS, BRAF, and HER2 alterations and the practical challenges of reflexive testing when patients are referred after undergoing biopsy elsewhere.

The panel also considers how tumor sidedness and molecular subtype influence first-line therapy. Left-sided, RAS and BRAF wild-type tumors may be approached differently from BRAF-mutated disease or tumors without an actionable biomarker. Dr. Fakih emphasizes that molecular findings must still be considered alongside patient age, performance status, disease burden, treatment goals, and whether oligometastatic disease may allow for surgical intervention. The episode highlights how precision medicine has added important new layers to first-line treatment planning while reinforcing the need to individualize therapy for each patient.

In the next episode, “Choosing a First-Line Chemotherapy Backbone and Maintenance Strategy in mCRC,” the panel discusses factors that influence chemotherapy selection and approaches to maintenance therapy.IIn this episode, “Choosing a First-Line Chemotherapy Backbone and Maintenance Strategy in mCRC,” the panel explores how clinicians select between standard chemotherapy backbones and plan for maintenance treatment in metastatic colorectal cancer.