How PET Imaging Agents Get FDA Approved: The Drug-Device Hybrid

PET imaging agents are neither drugs nor devices. They are a regulatory hybrid that follows a unique FDA approval pathway most biotech investors have never heard of. Understanding this pathway is essential for evaluating companies like Lantheus (LNTH), which closed at $101.50 with a market cap of $6.6 billion.

What is a PET imaging agent?

A PET (positron emission tomography) imaging agent is a molecule tagged with a radioactive isotope (F-18, Ga-68, or C-11) that emits positrons detected by a PET scanner. In plain English: it is a GPS tracker for disease. The radioactive tag makes it visible on a scan. The molecule determines where it goes.

For prostate cancer, a PSMA-PET agent binds to prostate-specific membrane antigen and lights up prostate cancer cells wherever they have spread. For Alzheimer’s, an amyloid-PET agent binds to amyloid plaques and confirms the diagnosis. For neuroendocrine tumors, a somatostatin receptor agent locates tumors that are invisible on CT scans.

The drug-device hybrid problem

PET agents are regulated as drugs (NDA pathway), but they are manufactured in cyclotrons and radiopharmacies, not traditional drug factories. The manufacturing challenge is unique: the radioactive isotope decays continuously. F-18 has a half-life of 110 minutes. Ga-68 has a half-life of 68 minutes. Every dose must be manufactured, quality-tested, transported, and injected within a window measured in hours.

Manufacturing consistency (dose calibration, radiochemical purity, stability over the half-life) is the regulatory challenge. For a traditional drug, a batch that fails quality control can be held and retested. For a PET agent, the batch decays while you are testing it. This is why manufacturing IS the approval hurdle for PET agents.

The approval pathway

The FDA approval pathway for PET agents has three phases:

Phase 1 (dosimetry and safety): The agent is injected into a small number of healthy volunteers to measure radiation exposure, biodistribution, and safety. This is not efficacy testing. It is pharmacokinetics and radiation dosimetry.

Phase 2 (diagnostic accuracy): The agent is tested in patients with known disease versus healthy controls to measure sensitivity and specificity. Can it detect cancer? Does it produce false positives?

Phase 3 (clinical utility): The FDA requires evidence that accurate diagnosis leads to better patient management. This is the critical difference from drug approvals. A PET agent must show not just that it detects disease, but that detecting disease changes what doctors do and that the change improves outcomes.

The gold standard: PYLARIFY

Lantheus’s PYLARIFY (F-18 DCFPyL) was approved in 2021 for PSMA-positive prostate cancer imaging. The Phase 3 CONDOR trial showed correct localization of prostate cancer lesions in 84.8-87.0% of cases. This is the textbook example of how a PET agent gets approved.

PYLARIFY is now the market leader in PSMA-PET imaging. Every prostate cancer patient suspected of metastatic disease gets a PSMA-PET scan before treatment planning. The recurring revenue model is attractive: every scan requires a dose of PYLARIFY, and prostate cancer monitoring involves multiple scans over the treatment journey.

For context on the broader diagnostics sector, see our diagnostics and liquid biopsy roundup.

The CRL example: LNTH-2501

Lantheus’s LNTH-2501 (Ga-68 edotreotide) for neuroendocrine tumor imaging received a complete response letter (CRL) in June 2026. The CRL cited manufacturing deficiencies, not efficacy concerns. This is the unique risk of PET agent investing: the science works, the trial succeeds, and the manufacturing process fails the FDA inspection.

The CRL illustrates the core thesis: for PET agents, manufacturing IS the regulatory hurdle. Companies that control their cyclotron and radiopharmacy infrastructure have a structural advantage. Companies that rely on third-party manufacturing face inspection risk. For background on CRLs, see our complete response letter explainer, and for NDA types, see our BLA vs NDA guide.

The isotope supply chain

F-18 (110-minute half-life) requires local cyclotrons. A hospital must be within roughly 2 hours of a cyclotron facility. Ga-68 (68-minute half-life) can be generator-produced, meaning a hospital can buy a Ga-68 generator and produce the isotope on-site without a cyclotron. The supply chain determines commercial viability.

PYLARIFY uses F-18, which limits distribution to cyclotron-adjacent sites. Ga-68 PSMA-11, produced by some academic centers, is available at no cost as a research reagent. This creates a generic competition dynamic that PYLARIFY must justify through convenience and consistency.

Investment implications

PET agents have lower revenue ceilings than therapeutic drugs but faster development timelines (typically 3-5 years versus 8-10 for therapeutics). The recurring revenue model is attractive: every scan needs a new dose. But generic competition from academic centers and reimbursement risk are structural threats.

Lantheus at $6.6 billion is the pure-play public company in this space. PYLARIFY revenue is growing, but the LNTH-2501 CRL shows the manufacturing risk is real. The company’s tau-PET program for Alzheimer’s imaging is the next growth driver. For context on the Lantheus acquisition landscape, see our Lantheus acquisition analysis.

The PET agent playbook is repeating across companies: NDA, manufacturing inspection, approval or CRL. Lantheus just showed us what the CRL path looks like. The next test is whether the tau-PET program clears the same hurdle.

Source: FDA, PYLARIFY approval labeling