October 17, 2026 · Oncology
Imagine being able to identify cancer cells throughout a patient's body, determine whether a particular treatment can reach them, and then use essentially the same targeting mechanism to deliver a radioactive payload directly to those cells.
That is the promise of theranostics, a term combining therapeutics and diagnostics. [1]
It sounds like science fiction. But important elements of this technology are already being used to treat cancer patients, and researchers are investigating whether the same approach can work across a much broader range of diseases.
First, how does it work?
Traditional cancer treatment often involves compromises. Chemotherapy circulates throughout the body, attacking rapidly dividing cells, including healthy ones. External-beam radiation can precisely target known tumors, but treating cancer that has spread to numerous locations presents additional challenges.
Theranostics takes a different approach.
Many cancer cells express particular proteins, or receptors, on their surfaces. Researchers can design molecules that recognize and bind to those targets.
Think of this molecule as a delivery vehicle programmed to recognize a particular address.
Step 1: Find the cancer.
Scientists attach a small amount of a radioactive imaging isotope to the targeting molecule. After injection, the molecule circulates throughout the body and accumulates in tissues expressing the target.
A PET scan can then reveal where that radioactive tracer has collected.
Importantly, this does more than simply show the location of a tumor. It provides evidence that the tumor expresses the molecular target the proposed treatment is designed to recognize. A positive scan helps select patients; it does not guarantee that every lesion will receive enough treatment or that an individual patient will benefit.
Step 2: Treat what we have found.
Now comes the clever part.
Researchers use the same or a closely related targeting molecule, but attach a different radioactive isotope — one capable of delivering a destructive dose of radiation.
Instead of primarily producing a signal for imaging, the resulting drug delivers radiation that can damage the DNA of nearby cancer cells and ultimately kill them.
The targeting molecule acts as the address label. The radioactive isotope provides the payload.
Step 3: Evaluate the response.
Subsequent imaging and clinical assessments help determine whether treatment is working, whether the cancer is progressing, and whether additional therapy might be appropriate.
In principle, this creates a powerful feedback loop between diagnosis, patient selection, treatment, and response assessment.
Why is this different from conventional radiation?
The distinction is important.
External-beam radiation directs energy toward a known anatomical location. Theranostic radiopharmaceuticals deliver radioactive material through the bloodstream, using molecular targeting to concentrate treatment in selected tissues.
This means that several tumors in different parts of the body may be treated simultaneously, including some that are too small or poorly located for conventional local treatment.
It does not mean that healthy tissues receive no radiation. They can, and do. The objective is to deliver substantially more biologically effective radiation to tumors than to vulnerable normal tissues.
That balance is central to whether a treatment succeeds. [2]
This is not just theoretical
Two established examples demonstrate that theranostics has already moved beyond the laboratory.
Prostate cancer: A drug called Pluvicto targets prostate-specific membrane antigen, or PSMA, a protein frequently expressed by prostate cancer cells. A PSMA PET scan helps identify suitable patients, while the therapeutic drug uses lutetium-177 to deliver radiation to PSMA-expressing tissue.
Initially approved in 2022, Pluvicto received additional FDA approvals in March 2025 and July 2026, extending its use into earlier treatment settings for certain patients. [3] [4] [5]
Neuroendocrine tumors: Lutathera uses a targeting molecule that binds somatostatin receptors, which are abundant on many neuroendocrine tumors. It also delivers lutetium-177.
In the NETTER-2 trial, patients with newly diagnosed, advanced, well-differentiated grade 2–3 gastroenteropancreatic neuroendocrine tumors receiving Lutathera with octreotide experienced median progression-free survival of 22.8 months, versus 8.5 months for those receiving high-dose octreotide alone. Progression-free survival measures time without disease progression or death; it is not the same as overall survival. [6]
Those are meaningful clinical results, not merely evidence of an interesting scientific mechanism.
The next frontier: Alpha particles
Many established radioligand treatments use isotopes such as lutetium-177, which emits beta particles.
Researchers are increasingly investigating alpha-emitting isotopes, including actinium-225.
Alpha particles deposit substantial energy over very short distances. That creates the possibility of inflicting severe DNA damage on cancer cells while limiting how far individual particles travel through surrounding tissues.
But the same potency presents challenges: delivering too much radiation to healthy organs can cause serious injury.
The real objective is not simply to create a more powerful radioactive payload. It is to improve the ratio of tumor destruction to normal-tissue toxicity.
In October 2026, Bristol Myers Squibb reported positive late-stage results for an investigational actinium-225 therapy in neuroendocrine tumors previously treated with lutetium-based therapy. The October 12 announcement concerned RYZ101 in the phase 3 ACTION-1 trial and reported an improvement in progression-free survival. These are sponsor-reported topline findings; detailed clinical results are still needed to evaluate the magnitude of benefit and the safety tradeoffs. [7]
So why is everyone getting excited?
Because theranostics potentially addresses several persistent problems in oncology at once.
It can improve patient selection by showing whether tumors express the intended target. It can treat disease distributed throughout the body rather than at just one location. And it creates opportunities to adapt treatment based on measurable biological information.
Perhaps most importantly, it represents a shift from asking only, "What kind of cancer does this patient have?" toward asking, "What molecular features does this patient's cancer have, and can we exploit them?"
But there are substantial obstacles.
Not every tumor expresses a useful target. Even within one patient, different tumors may express that target at different levels. Some normal organs can accumulate the drug, potentially damaging the kidneys, salivary glands, or bone marrow. [3] [8]
Radioactive isotopes can also be difficult to manufacture, transport, and distribute. Some decay rapidly, creating unusually demanding supply-chain requirements.
And demonstrating that an experimental agent binds to a tumor is not equivalent to demonstrating that it improves survival or quality of life.
The bigger picture
For decades, oncology has been moving toward greater precision through molecular diagnostics, targeted drugs, immunotherapies, and genetic profiling.
Theranostics adds another capability: the ability to link molecular imaging directly to a targeted treatment.
We are not yet at the point where clinicians can map every cancer cell and eliminate it without collateral damage. Tumor heterogeneity, biological resistance, and treatment toxicity remain formidable problems.
Nevertheless, the concept is compelling.
Instead of administering a treatment and hoping it reaches the disease, we may increasingly be able to demonstrate where the treatment is likely to go before delivering the therapeutic payload.
That is a genuinely important development — and one worth following.
Science Explained explores emerging technologies, medical discoveries, and the biological principles behind them. Its purpose is to make complex science understandable without oversimplifying the uncertainties that remain.
Sources and evidence notes
Evidence checked October 17, 2026. Regulatory approvals apply to defined patient populations; trial outcomes are not guarantees for an individual patient.
- SNMMI: What is Theranostics? Diagnostic imaging, patient selection and paired treatment.
- NCI: Radiation Therapy Enters the Molecular Age (2020). Targeting, radiation delivery, clinical development and practical limitations.
- FDA: Pluvicto original approval snapshot (2022). Original approval and trial population.
- FDA: Pluvicto indication expansion, March 28, 2025. Selected PSMA-positive, previously treated metastatic castration-resistant disease before taxane chemotherapy.
- FDA: Pluvicto approval with androgen receptor pathway inhibitor therapy, July 31, 2026. Selected PSMA-positive metastatic androgen pathway modulation-naïve or -sensitive prostate cancer.
- Singh et al., The Lancet (2024): NETTER-2. Randomized phase 3 study; population, comparator and progression-free survival results.
- Bristol Myers Squibb: ACTION-1 interim topline announcement, October 12, 2026. Sponsor-reported results for investigational actinium-225 therapy after lutetium-based treatment; not a full peer-reviewed report.
- Lutathera prescribing information, DailyMed. Mechanism, radiation precautions, bone marrow suppression and organ toxicity.