Tumor Heterogeneity and Lesion-Specific Response to Targeted Therapy in Colorectal Cancer

TLDR

Genomic heterogeneity linked to acquired resistance to targeted agents and its impact on subsequent therapy responses remains unknown. The study aimed to evaluate whether combining tissue and liquid biopsies with imaging can monitor lesion‑specific responses to EGFR blockade in colorectal cancer. The authors performed EGFR blockade trials in colorectal cancer, integrating tissue and liquid biopsies with radiologic imaging to track lesion‑specific responses to oncogenic alterations. Parallel tumor biopsy and serial ctDNA analyses revealed that distinct resistance mechanisms—such as a MEK1(K57T) mutation and a KRAS(Q61H) mutation—drive lesion‑specific responses, demonstrating that single‑lesion biopsies are insufficient and ctDNA can detect concurrent resistance across metastases.

Abstract

How genomic heterogeneity associated with acquired resistance to targeted agents affects response to subsequent therapy is unknown. We studied EGFR blockade in colorectal cancer to assess whether tissue and liquid biopsies can be integrated with radiologic imaging to monitor the impact of individual oncogenic alterations on lesion-specific responses. Biopsy of a patient's progressing liver metastasis following prolonged response to cetuximab revealed a MEK1(K57T) mutation as a novel mechanism of acquired resistance. This lesion regressed upon treatment with panitumumab and the MEK inhibitor trametinib. In circulating tumor DNA (ctDNA), mutant MEK1 levels declined with treatment, but a previously unrecognized KRAS(Q61H) mutation was also identified that increased despite therapy. This same KRAS mutation was later found in a separate nonresponding metastasis. In summary, parallel analyses of tumor biopsies and serial ctDNA monitoring show that lesion-specific radiographic responses to subsequent targeted therapies can be driven by distinct resistance mechanisms arising within separate tumor lesions in the same patient.Molecular heterogeneity ensuing from acquired resistance drives lesion-specific responses to subsequent targeted therapies. Analysis of a single-lesion biopsy is inadequate to guide selection of subsequent targeted therapies. ctDNA profiles allow the detection of concomitant resistance mechanisms residing in separate metastases and assessment of the effect of therapies designed to overcome resistance.