Molecular Profiling in Oncology

The discovery of activating EGFR mutations in non-small cell lung cancer (NSCLC) in 2004 inaugurated the era of molecularly targeted oncology. Initially, molecular testing in pathology was limited to single-gene assays—EGFR mutation testing for gefitinib/erlotinib eligibility, KRAS testing for anti-EGFR antibody exclusion in colorectal cancer, and BRAF V600E testing for melanoma. Each new targetable alteration required a separate test, consuming precious tissue and extending turnaround times. The recognition that dozens of actionable genomic alterations existed across cancer types, combined with limited biopsy material, created an urgent need for multiplexed testing platforms that could interrogate many genes simultaneously from a single sample.

Next-generation sequencing (NGS) panels transformed molecular pathology by enabling simultaneous interrogation of hundreds of genes from a single tissue sample. FoundationOne CDx received FDA approval in 2017 as the first comprehensive genomic profiling (CGP) test, analyzing 324 genes plus microsatellite instability (MSI) and tumor mutational burden (TMB). The MSK-IMPACT panel, validated at Memorial Sloan Kettering, became the first tumor profiling test authorized by the FDA through the New York State Department of Health. Large-scale genomic studies including TCGA (The Cancer Genome Atlas) and AACR Project GENIE provided the reference databases needed to interpret variants of unknown significance. CGP became the standard of care for advanced NSCLC, with studies showing that broad-panel NGS identified actionable alterations in 64% of patients.

The emergence of tumor-agnostic biomarkers represented a fundamental shift in oncology from organ-based to biomarker-based treatment. The FDA's 2017 approval of pembrolizumab for MSI-H/dMMR solid tumors regardless of histology was the first tumor-agnostic approval in oncology history. This was followed by larotrectinib for NTRK fusion-positive cancers in 2018 and pembrolizumab for TMB-high tumors in 2020. The KEYNOTE-158 trial established TMB-high (>=10 mut/Mb) as a predictive biomarker across tumor types. These approvals fundamentally changed the role of molecular pathology from confirming a suspected diagnosis to discovering therapeutic targets that would not have been identified by histology alone. RNA-based gene expression profiling tests (Oncotype DX, MammaPrint) became integral to treatment decisions, with the TAILORx and MINDACT trials validating their role in sparing chemotherapy.

Molecular profiling is now embedded in clinical guidelines across all major cancer types. The NCCN guidelines recommend CGP for advanced NSCLC, and broad molecular testing for many advanced solid tumors. The ESMO Scale for Clinical Actionability of molecular Targets (ESCAT) provides a tiered framework for interpreting genomic findings. The CAP/IASLC/AMP molecular testing guideline for NSCLC was updated to recommend broad panel NGS over sequential single-gene testing. WHO Classification of Tumours (5th edition) has integrated molecular features into the diagnostic criteria for many tumor types, blurring the line between anatomic and molecular pathology.

Molecular profiling has become the cornerstone of precision oncology. Whole-genome sequencing and whole-transcriptome sequencing are entering clinical practice for cases where panel-based approaches are insufficient. Pharmacogenomic testing is expanding beyond somatic mutations to include germline variants affecting drug metabolism. Spatial transcriptomics and single-cell sequencing are providing insights into tumor heterogeneity and the tumor microenvironment. The integration of molecular data with digital pathology through AI is enabling multi-modal biomarker discovery. Key challenges include equitable access to genomic testing, managing the increasing complexity of molecular data interpretation, variant reclassification, and ensuring turnaround times compatible with clinical decision-making. Molecular tumor boards have become essential for translating complex genomic findings into treatment recommendations.