Cancer diagnostics are undergoing a fundamental shift away from single-gene testing toward comprehensive molecular profiling that examines multiple layers of tumor biology simultaneously. Clinical laboratories are now adopting whole-genome sequencing, functional RNA analysis, liquid biopsy, and multi-omic testing to provide a more complete picture of how a tumor behaves and how it will respond to treatment.

Why Are Single-Gene Tests No Longer Enough?

For decades, cancer diagnosis relied on identifying one mutation in one gene. But that approach misses critical information. A recent study by Inocras, a precision oncology company, found that about 21% of patients with ovarian cancer who tested negative for BRCA mutations were actually positive for homologous recombination deficiency, a genetic signature that predicts response to certain therapies. Those patients would have been missed by BRCA-only testing, potentially losing access to treatments that could extend their survival.

"We are moving well beyond the traditional approach of testing a single mutation in a single gene," said Luca Quagliata, corporate head of diagnostic medical and scientific affairs for the products and technology sector at Thermo Fisher Scientific.

Luca Quagliata, Corporate Head of Diagnostic Medical and Scientific Affairs, Thermo Fisher Scientific

The problem is that DNA mutations alone often don't tell the full story. Most tumors lack actionable mutations, and even those that do can develop resistance as they evolve under treatment. Gene expression profiling, which examines which genes are actually active in a tumor, offers another lens for understanding disease and guiding treatment decisions.

What Layers of Information Are Doctors Now Analyzing?

Modern cancer diagnostics now examine multiple dimensions of tumor biology in a single test:

• DNA-level alterations: Mutations, methylation patterns, and structural variants that reveal genetic changes in cancer cells
• RNA-level changes: Gene fusions, expression profiles, and other molecular signals that show which genes are actively driving the tumor
• Protein analysis: Proteomic data that reveals which biological pathways are actually active, not just which receptors are present
• Blood-based testing: Liquid biopsy approaches that detect tumor signals in blood samples, enabling repeated monitoring without invasive tissue biopsies

Whole-genome sequencing exemplifies this broader approach. Instead of testing genes one at a time, laboratories can now sequence an entire genome in a single test and identify multiple types of alterations, including driver mutations, structural variants, germline variants, and genomic signatures like homologous recombination deficiency. National initiatives in the United Kingdom and Netherlands have demonstrated that whole-genome sequencing can be integrated into routine clinical care while matching the turnaround times of older, narrower panel-based approaches.

One key insight from Agendia, a molecular diagnostics company, highlights why functional analysis matters. Standard pathology checks whether a receptor is physically present on a cancer cell using immunohistochemistry. But presence alone doesn't guarantee the receptor is driving tumor growth. Agendia's approach evaluates functional RNA expression to identify which biological pathways are actually active. The company found that this method reclassifies nearly 30% of estrogen receptor-positive, HER2-negative breast cancers, identifying some that behave like more aggressive tumor types.

How Are Doctors Using Gene Expression to Guide Treatment?

Gene expression profiling is moving beyond tumor characterization into active treatment planning. Earlier this year, Agendia reported data from its FLEX Study showing that its tests can identify which patients with hormone receptor-positive, HER2-negative early-stage breast cancer are most likely to benefit from anthracycline-based chemotherapy, a prediction that standard pathology cannot make.

"The future will not be tissue versus liquid biopsy. It will be about using the right sample, at the right time, for the right clinical question, and enabling a more dynamic, longitudinal view of the patient's disease," said Luca Quagliata.

Luca Quagliata, Corporate Head of Diagnostic Medical and Scientific Affairs, Thermo Fisher Scientific

This shift reflects a broader recognition that cancer is not static. Historically, molecular testing was treated as a snapshot taken at diagnosis. But the future of precision oncology requires continuous monitoring. Minimal residual disease detection, recurrence monitoring, and treatment resistance all require clinicians to understand how disease biology changes over time.

How Is Monitoring Changing Cancer Care?

Liquid biopsy and alternative sampling methods are making repeated testing more practical. Blood-based testing expands access to molecular profiling when tissue is limited and makes repeat testing realistic without invasive procedures. One example comes from research at the Fred Hutchinson Cancer Center, where investigators demonstrated that next-generation sequencing of chronic myeloid leukemia can be completed using a simple dried blood spot, eliminating the need for cold shipping and laboratory phlebotomy. The researchers detected ABL1 mutations that could guide therapy in roughly one-third of patients while also identifying additional pathogenic variants.

Platforms like Inocras' MRDVision illustrate how testing is moving toward continuous assessment across the patient journey. These tools use whole-genome information to detect and monitor molecular residual disease while reducing the likelihood of missing tumor signals that fall outside preselected targets.

Steps to Understanding Your Cancer Diagnostic Options

• Ask about comprehensive testing: When diagnosed with cancer, ask your oncologist whether comprehensive genomic profiling, whole-genome sequencing, or gene expression testing is available and appropriate for your tumor type
• Understand the difference between presence and function: A receptor being present on a cancer cell does not guarantee it is driving tumor growth; functional testing reveals which biological pathways are actually active
• Plan for longitudinal monitoring: Discuss with your care team whether liquid biopsy or blood-based testing could be used to monitor your disease over time, rather than relying on a single diagnostic test
• Consider the value beyond upfront cost: While narrower assays may appear less expensive initially, comprehensive testing that identifies clinically actionable findings can prevent additional testing, delays, and unnecessary use of limited tissue samples

The shift toward comprehensive molecular profiling reflects a fundamental change in how oncologists understand cancer. Rather than viewing tumors as defined by a single mutation, clinicians now recognize that understanding tumor biology requires examining multiple layers of genetic and molecular information, monitoring how that biology changes over time, and using that knowledge to guide personalized treatment decisions.