Comparison of genomic profiling of patient-matched primary colorectal and surgical resected distant metastatic (stage IV) colorectal carcinoma for drug actionability

It is often difficult to obtain adequate tissue for genomic study from distant metastases for assessment of targeted therapy in colorectal carcinomas. The study aims to explore the genomic differences between matched distant metastatic colorectal carcinomas (mCRC) and primary carcinoma using surgical specimens of both with adequate tissue. Thirty-four paired primary and distant metastatic colorectal carcinoma samples (liver, ovary, and lung) were obtained from surgical excisions (not small biopsies) and are microsatellite stable. They were subjected to DNA sequencing using comprehensive next-generation sequencing. This included mutation concordance analysis and mutational signature analysis. The mutation concordance analysis showed 49.6% shared mutations between primary and metastatic tumours, with 23.0% mutations exclusive to primary tumours and 27.4% mutations exclusive to distant metastases. While many patients with KRAS/BRAF mutations had shared mutations, two cases had unique KRAS mutations in the primary tumours only. Additionally, TMB (tumour mutational burden) analysis revealed that half of the TMB-high (≥7.5 mutations/Mb) metastatic colorectal carcinomas had a low TMB (<7.5 mutations/Mb) in the primary tumours. The mutational signature analysis identified de novo signatures consistent with known single base substitution patterns such as SBS11 (alkylation agents) and SBS30 (base excision repair deficiency) post-chemotherapy. To conclude, this study demonstrates significant genomic variations in resected distant metastasis when compared to primary colorectal carcinomas when adequate tissue is available. This finding underscores the importance of considering these differences and selecting tissue for mutation analysis in planning targeted and effective treatment strategies for mCRC.