In precision oncology, a targeted drug is only as accessible as the companion diagnostic test that identifies eligible patients. For over two decades, the Food and Drug Administration classified in situ hybridization (ISH and FISH) companion diagnostic tests as Class III medical devices, subjecting them to the same rigorous Premarket Approval (PMA) pathway reserved for high-risk implantable pacemakers and artificial heart valves.

As of today, September 16, 2026, the FDA's final administrative order officially downclassifies these vital cancer diagnostics into Class II devices subject to 510(k) premarket notification and special controls. By codifying this change under 21 CFR 864.1890, the FDA is fundamentally transforming diagnostic development economics, moving the devices from PMA review to 510(k) premarket notification with special controls and reducing regulatory burden for future entrants.

In this deep dive, we are going to look at:

  • Why this matters now: Eliminating the companion diagnostic bottleneck
  • What actually happened: Analysis of the 21 CFR 864.1890 final rule and affected product codes
  • The obvious read versus the deeper signal: The shift from PMA monopolies to commoditized assay competition
  • Comparison framework: Legacy Class III PMA vs New Class II 510(k) Special Controls
  • The Evidence Ladder: Analytical validation, concordance standards, and clinical utility
  • The HealthTech Investor's Signal: Valuation impacts on diagnostic incumbents vs agile tooling startups
  • Operational counter-thesis: Quality risks and the threat of substandard decentralized assays
  • Forward intelligence: 4 observable test milestones across 2026 to 2028
  • The Bottom Line for Oncology Executives and Diagnostics Developers

Why this matters now

Targeted cancer therapies, such as HER2 inhibitors in breast cancer and ALK/ROS1 inhibitors in non-small cell lung cancer, rely heavily on in situ hybridization to detect gene amplifications and chromosomal rearrangements. Under the legacy Class III framework, bringing a new ISH companion test to market required a full PMA application, carrying user fees exceeding $500,000, multi-volume technical dossiers, and mandatory pre-approval facility inspections.

Even more burdensome for diagnostic manufacturers were the requirements for post-approval lifecycle management. Any minor modification to probe chemistry, antibody binding reagents, or automated staining instrumentation required a formal PMA supplement, taking months to clear. Consequently, many innovative diagnostic startups chose not to enter the companion diagnostic market, leaving testing concentrated among a handful of legacy multinational diagnostic conglomerates.

A fluorescence microscopy workstation displays chromosome probe signals used in molecular diagnostics.
A fluorescence microscopy workstation displays chromosome probe signals used in molecular diagnostics.

What actually happened

The final order was published on August 17 and took effect September 16, 2026.

The FDA codified its final administrative order in the Federal Register, creating 21 CFR § 864.1890: In Situ Hybridization Test Systems for Use with a Corresponding Approved Oncology Therapeutic Product.

The order formally covers four existing oncology companion-diagnostic product codes: NYQ, MVD, OWE, and PNK.

Under the new Class II regime, manufacturers can seek clearance through a 510(k) by demonstrating substantial equivalence and satisfying special controls covering analytical and clinical performance, labeling, and reproducibility.