Cancer testing does not work the way most people expect. There is no test a physician orders that comes back with a definitive yes or no — no result that tells a patient, with certainty, whether cancer is present or absent. Instead, diagnosis unfolds across a workflow of accumulating evidence: screening signals that flag elevated risk, imaging studies that locate suspicious masses, tissue biopsies that characterize cellular morphology, and molecular tests that identify genetic drivers. Each layer adds information. None is sufficient on its own.
This is not a gap waiting to be closed by better technology. It reflects something fundamental about cancer biology — the heterogeneity of tumor cells, the overlap between malignant and benign presentations, and the reality that early-stage cancers may produce almost no measurable signal at all. Understanding why oncology diagnostics is inherently difficult is essential for anyone operating in the space: whether in test development, regulatory strategy, commercial planning, or clinical care.
Cancer Is Not a Single Disease
The word cancer encompasses hundreds of biologically distinct diseases that happen to share a common mechanism — uncontrolled cell growth. Lung adenocarcinoma behaves differently from lung squamous cell carcinoma. Triple-negative breast cancer has a different biology, prognosis, and treatment landscape than HER2-positive breast cancer. Glioblastoma multiforme is not one tumor type but a collection of molecularly distinct subtypes that respond differently to treatment.
This heterogeneity creates a fundamental challenge for diagnostic test design. A screening test that performs well across all subtypes of a given cancer type may not exist. A biomarker that reliably detects one subtype may be absent or expressed at low levels in another. And as tumors evolve under treatment pressure, the molecular profile of a cancer at diagnosis may differ substantially from its profile at relapse — meaning a test that was informative initially may need to be repeated, and may return different results.
| Diagnostic Stage | Clinical Objective | Primary Test Types | Evidentiary Standard | MKA Strategic Implication |
|---|---|---|---|---|
| Early Detection / Screening | Identify cancer signals in asymptomatic individuals; find disease before symptoms appear | MCED liquid biopsy, PSA, mammography, low-dose CT (lung), colonoscopy, HPV testing | Analytical + clinical validity required; clinical utility bar is highest here — payers demand outcome evidence before coverage | MCED tests face the most demanding evidentiary path in oncology diagnostics. Payers are watching the clinical utility evidence accumulate before making coverage commitments. The first MCED test to achieve guideline inclusion will reshape the market — and the race is active. |
| Formal Diagnosis | Confirm presence and characterize the disease; establish tumor type, grade, and stage | Tissue biopsy + pathology, IHC/FISH, NGS tumor profiling, liquid biopsy (when tissue inaccessible) | Tissue biopsy remains gold standard; liquid biopsy increasingly used as complement for characterizing metastatic spread | Tissue access limitations — driven by tumor location, patient fragility, or metastatic distribution — are the primary commercial driver of liquid biopsy adoption at the diagnosis stage. Tests that can reliably characterize molecular profile from blood in tissue-inaccessible cases carry disproportionate clinical and commercial value. |
| Treatment Selection | Identify which therapy is appropriate for this patient’s tumor biology; confirm CDx eligibility | CDx-linked biomarker testing (EGFR, BRCA, RAS, PD-L1, TMB, MSI), comprehensive NGS panels, pharmacogenomics | Highest commercial value stage; CDx CAGR >10%; FDA-cleared CDx now required or strongly recommended for most targeted therapies | This is where diagnostic commercial value is most concentrated. A positive CDx result directly unlocks access to a high-cost targeted therapy — making this stage the primary focus of payer scrutiny, coverage negotiation, and reimbursement strategy. Companies developing CDx programs need to engage payers early, not after approval. |
| Monitoring & MRD | Track treatment response; detect resistance or minimal residual disease; guide surveillance | Serial ctDNA / liquid biopsy, CEA/CA-19-9 (colorectal/pancreatic), imaging (PET, CT), CTC counts | Fastest-growing application for liquid biopsy; MRD detection now FDA-accepted endpoint in several hematologic malignancies | Serial testing creates a recurring revenue model that tissue biopsy cannot replicate. The clinical case for earlier intervention based on ctDNA MRD signal is strong mechanistically — the remaining evidentiary gap is demonstrating that earlier intervention changes outcomes, not just biomarker curves. This gap is actively closing. |
Clinical staging framework based on published oncology diagnostic literature and FDA guidance. Evidentiary standards reflect current FDA and payer coverage criteria. Strategic implications reflect MKA Insights analytical framework.
The Four-Stage Diagnostic Workflow
Oncology diagnostics are typically organized around four sequential objectives: early detection, formal diagnosis, treatment selection, and monitoring. Each stage has distinct testing requirements, performance standards, and clinical stakes.
1. Early Detection and Screening
Screening tests check for cancer signals in people who have no symptoms. The goal is to identify disease early, when treatment is most likely to be effective. Common screening tools include PSA testing for prostate cancer, mammography for breast cancer, colonoscopy for colorectal cancer, and low-dose CT for lung cancer in high-risk populations.
The critical limitation of screening tests is that they are not designed to detect cancer — they are designed to identify elevated risk or suspicious findings that warrant further investigation. A positive PSA result does not mean a patient has prostate cancer. It means prostate cancer cannot be excluded without additional testing. False positives create anxiety, lead to unnecessary biopsies, and generate costs. False negatives create false reassurance. Calibrating the sensitivity and specificity of a screening test is a clinical and regulatory challenge that has no clean solution.
Multi-cancer early detection (MCED) tests — which screen for signals from multiple cancer types simultaneously using a single blood draw — represent the frontier of this challenge. These tests analyze circulating tumor DNA and other biomarkers to detect cancer signals across dozens of cancer types at once. The clinical evidence is still maturing, and guideline inclusion remains limited, but the science is advancing rapidly.
2. Formal Diagnosis
Once a screening result or symptom prompts further investigation, the diagnostic process moves toward formal confirmation. For most solid tumors, this requires tissue — a biopsy that allows pathologists to examine cellular morphology, staining characteristics, and increasingly, molecular features of the tumor itself.
Tissue biopsy is the diagnostic gold standard, but it is not without limitations. Access depends on tumor location — biopsying a lesion adjacent to the aorta carries different procedural risk than biopsying a superficial lymph node. A small biopsy may not capture the full heterogeneity of the tumor. And repeat biopsies, which are sometimes needed to track disease evolution or confirm relapse, carry cumulative procedural burden.
Liquid biopsy is increasingly used as a complement to tissue biopsy in formal diagnosis, particularly when tissue is difficult to obtain or when characterizing the molecular profile of disease that has spread beyond the primary site. However, liquid biopsy cannot replace tissue in most diagnostic algorithms — it can characterize the genetic profile of circulating tumor material, but it cannot confirm cellular architecture or grade the histopathological features that define stage and subtype.
3. Treatment Selection
For many cancers, a confirmed diagnosis is followed immediately by a question: which therapy, for this patient, at this stage? Molecular profiling of the tumor — identifying mutations, copy number alterations, gene fusions, and expression levels — has become standard practice in most major cancer types. These profiles determine eligibility for targeted therapies and, increasingly, for immunotherapies.
Companion diagnostics are the regulatory mechanism that formalizes this link between a molecular test result and a specific therapy. When the FDA approves a targeted therapy that only works in patients with a specific genetic alteration, it typically requires that the prescribing physician use an FDA-cleared companion diagnostic to confirm the presence of that alteration before treatment. As the targeted therapy landscape has expanded, the number of companion diagnostics in use has grown substantially.
Treatment selection testing is among the most commercially consequential diagnostic applications, because the clinical and commercial stakes are directly linked. A test that determines eligibility for a $100,000-per-year targeted therapy occupies a very different position in the care pathway — and in payer decision-making — than a routine screening test.
4. Monitoring and Surveillance
Routine monitoring tracks whether a therapy is working, whether disease is progressing, and whether a patient in remission is showing early signs of recurrence. This is where longitudinal testing — the ability to repeat a test over time and compare results — is most valuable.
Liquid biopsy is particularly well-suited to monitoring applications, because it can be repeated serially without repeated tissue access. Detecting a rise in circulating tumor DNA after a period of undetectable levels is a signal that disease may be recurring — often weeks or months before imaging findings would reveal it. This earlier detection window creates an opportunity to intervene sooner, though the clinical evidence for whether earlier intervention improves outcomes remains an active area of research.
Why the Difficulty Matters Commercially
The complexity of oncology diagnostics is not just a clinical fact — it has direct implications for market access, reimbursement, and commercial strategy. Payers increasingly require clinical utility evidence before agreeing to cover a test: not just that the test measures what it claims to measure (analytical validity), and not just that it accurately predicts the presence or absence of disease (clinical validity), but that using the test leads to better patient outcomes (clinical utility). This is a higher evidentiary bar, and it requires test developers to design and fund studies that go beyond traditional analytical and clinical validation.
The regulatory landscape adds another layer. The FDA regulates in vitro diagnostics under different frameworks depending on how they are developed and commercialized — a distinction that has become more complex following the FDA’s 2024 finalization of rules significantly expanding oversight of laboratory-developed tests. Understanding where a test sits in this regulatory architecture is foundational to any commercial strategy in the oncology diagnostics space.
Despite all of this complexity, oncology diagnostics remains one of the most commercially attractive segments in all of healthcare — because the clinical need is acute, the therapy pipeline is deep, and the value of a test that reliably guides treatment selection in a high-cost disease area is substantial. The difficulty is real. So is the opportunity.