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Companion Diagnostics

Diagnostic tests determining therapy eligibility–where functional biomarkers reveal patients missed by expression-based companion diagnostics.

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Definition
Companion diagnostics are FDA-regulated tests that identify patients eligible for specific therapies. Current CDx for checkpoint inhibitorsLoading... rely on expression (PD-L1 IHCLoading...), missing patients with low expression but active checkpoint engagement. QF-ProLoading... functional biomarkersLoading... could expand therapy eligibility by identifying patients based on interaction state rather than expression level.
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The 2.13% Clinical Cutoff
Primary
Related Segments
HER2/EGFR/HER3 Interactions in HNSCC
Related
FDA-regulated
Requires analytical + clinical validation
Therapy gating
Determines treatment eligibility
Current gap
Expression ≠ response
Expansion opportunity
Function-based eligibility

The Regulatory Framework

Companion diagnostics occupy a unique regulatory category. Unlike standalone laboratory tests, CDx are co-developed with specific therapeutic agents and reviewed by FDA alongside the drug approval.

The regulatory bar is high: CDx require demonstration of analytical validity (accurate, reproducible measurement) and clinical validity (correlation with therapeutic response). Bridging studies must show that the biomarker identifies patients who benefit from therapy while excluding those who do not.

Critically, FDA approval of a CDx creates a reimbursement pathway–CMS and private payers routinely cover FDA-approved companion diagnostics. This economic framework incentivizes CDx development and ensures clinical adoption.

The companion diagnostic paradigm has driven precision oncologyLoading... forward, but current CDx share a common limitation: most measure expression or mutation status, not functional protein engagement.

Simplified

What's Required: A companion diagnostic (CDx) is a test that must be used to select patients for a specific therapy. FDA approval requires proof that the test reliably identifies who should (or shouldn't) receive the drug.

Examples: HER2 testing for trastuzumab, EGFR testing for erlotinib, PD-L1 testing for pembrolizumab (in some indications).

The Eligibility Expansion Opportunity

Expression-based companion diagnostics systematically under-identify eligible patients. The clinical data are clear:

In checkpoint inhibitor therapy, patients classified as "PD-L1 negative" by IHC may still have active checkpoint engagement detectable by iFRETLoading.... These patients–currently denied therapy based on expression criteria–represent a missed treatment opportunity.

The inverse also occurs: patients meeting expression thresholds may lack functional engagement and fail to respond. Expression-based CDx cannot distinguish responders from non-responders within the "biomarker-positive" population.

Functional biomarker CDx could address both problems:

* Expand eligibility to low-expression patients with active engagement
* Improve prediction by identifying true responders among biomarker-positive patients
* Reduce futile treatment in patients without functional target engagement

The commercial opportunity is substantial: even modest improvements in patient selection translate to billions in healthcare value through improved outcomes and reduced treatment failures.

Simplified

The Current Gap: Most CDx tests measure expression. Patients labeled "negative" may actually have functional activity and could benefit from treatment.

QF-Pro Potential: Functional biomarker CDx could expand therapy eligibility by identifying responders among currently "ineligible" patients—like the 10/11 "PD-L1 negative" kidney cancer patients with detectable checkpoint engagement.

QF-Pro CDx Opportunity

Clinically Validated

Regulatory Foundation: QF-Pro has the validation foundation for CDx development:
• Analytical validity: FRET physics well-established
• Clinical validity: Outcome correlations (P=0.05[3] survival)
• FFPE compatibility: Standard clinical workflows

Key CDx opportunity: expanding therapy eligibility for "biomarker-negative" patients with functional engagement.

Click citation numbers to view full references in QF-Pro Applications & Clinical EvidenceLoading...

Simplified

CDx opportunity: QF-Pro has the foundation for companion diagnostics: validated physics, clinical correlations, FFPE compatibility. Key opportunity: expanding therapy access for "negative" patients who actually have functional engagement.

Clinical Validation for CDx Development

  • Retrospective validation: iFRETLoading... correlation with survival in melanomaLoading... and NSCLCLoading... provides the clinical validation foundation required for CDx development
  • FFPELoading... compatibility: QF-Pro operates on standard clinical samples, enabling validation using existing biobanked tissue with known outcomes
  • Quantitative output: fretLoading...-efficiency|FRET efficiency}} provides continuous numerical values compatible with regulatory cutpoint validation requirements
  • Established precedent: FDA has approved imaging-based companion diagnostics; FLIM-FRETLoading... represents a validated imaging modality with clear analytical validation pathway

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