Overview
Radioligand therapy (RLT)—also termed targeted radiopharmaceutical therapy or theranostics—has matured from a niche oncologic modality into a broad precision medicine platform. RLT combines a tumor-selective ligand (peptide, small molecule, or antibody) conjugated to a therapeutic radionuclide, enabling high-dose radiation delivery directly to cancer cells while limiting exposure to surrounding normal tissue 14. The defining theranostic principle—using a diagnostic radiotracer paired with a therapeutic isotope sharing near-identical biodistribution—allows clinicians to confirm target expression, select patients most likely to respond, and monitor treatment response before and during therapy 47. As of mid-2026, two major classes of RLT agents are established in clinical practice: prostate-specific membrane antigen (PSMA)-directed therapy in advanced prostate cancer, and somatostatin receptor subtype 2 (SSTR2)-directed therapy in gastroenteropancreatic neuroendocrine tumors (GEP-NETs). A rapidly expanding pipeline targets fibroblast activation protein (FAP), gastrin-releasing peptide receptor (GRPR), delta-like ligand 3 (DLL3), C-X-C chemokine receptor 4 (CXCR4), and other pan-tumor antigens 78.
Scientific and Clinical Overview
RLT operates through receptor-mediated endocytosis or surface binding: the targeting ligand binds a tumor-associated antigen, the radionuclide payload is internalized, and emitted ionizing radiation induces DNA double-strand breaks that overwhelm tumor cell repair capacity 425. Unlike external beam radiotherapy, RLT delivers systemic, molecularly guided radiation; unlike conventional chemotherapy or immunotherapy, it exploits tumor-specific receptor overexpression for selectivity. Compared with antibody-drug conjugates (ADCs), RLT leverages radiobiology—including cross-fire irradiation of adjacent PSMA-negative cells by beta emitters—rather than direct cytotoxic payloads. Patient selection depends critically on companion imaging: PSMA positron emission tomography (PET) with gallium-68 or fluorine-18 labeled tracers for prostate cancer, and SSTR PET for NETs, confirm sufficient target expression before treatment initiation 56.
Key Therapeutic Targets
Table 1. Key RLT Targets: Indication, Rationale, Clinical Maturity, and Limitations
| Target | Primary Indications | Biological Rationale | Clinical Maturity | Key Strengths | Key Limitations |
|---|---|---|---|---|---|
| PSMA (prostate-specific membrane antigen / FOLH1) | Metastatic castration-resistant prostate cancer (mCRPC); metastatic hormone-sensitive prostate cancer (mHSPC) | Transmembrane glycoprotein highly overexpressed on prostate cancer cells; rapid receptor-mediated internalization | Approved (FDA, EMA); multiple phase III trials | Robust PFS and OS data; validated companion imaging; multiple approved agents | Heterogeneous PSMA expression; PSMA-negative progression; xerostomia from salivary gland uptake |
| SSTR2 (somatostatin receptor subtype 2) | Progressive, unresectable/metastatic GEP-NETs (G1–G3) | Somatostatin receptors overexpressed on NET cells; receptor-mediated internalization | Approved (FDA, EMA); first-line expansion via NETTER-2 | Disease control and PFS benefit; established safety profile; amino acid co-infusion limits nephrotoxicity | Limited OS statistical significance (NETTER-1 crossover); restricted to SSTR-positive well-differentiated NETs |
| FAP (fibroblast activation protein alpha) | Multiple solid tumors (breast, sarcoma, thyroid, colorectal, and others) | FAP expressed on cancer-associated fibroblasts (CAFs) in >90% of epithelial malignancies; stromal remodeling may augment other therapies | Phase I–II; no regulatory approval retrieved | Pan-tumor applicability; complementary to PSMA/SSTR approaches | Early-phase evidence only; no randomized efficacy data; tumor biology reflects stromal rather than direct cell killing |
| GRPR (gastrin-releasing peptide receptor) | Prostate cancer; other solid tumors | Overexpressed on prostate cancer, especially androgen receptor–low/negative disease | Phase III (NeoB program) for prostate cancer | Potential utility where PSMA expression is low or absent | Phase III data not yet mature; comparative efficacy vs. PSMA-RLT not established |
| DLL3 (delta-like ligand 3) | Small-cell lung cancer (SCLC); neuroendocrine prostate cancer (NEPC) | Neuroendocrine lineage marker; high and relatively homogeneous expression in SCLC and NEPC | Preclinical to early translational; no clinical RLT data retrieved | Addresses unmet need in highly aggressive neuroendocrine cancers | Human RLT efficacy/safety data not yet available in retrieved materials |
| CXCR4 (C-X-C chemokine receptor 4) | Select NETs and neuroendocrine carcinomas (NECs) | CXCR4 overexpressed in certain NETs; enables radionuclide delivery to CXCR4-expressing disease | Early clinical; limited evidence | Niche utility in CXCR4-high NETs | Very limited quantitative clinical data retrieved; evidence immature |
| Integrins / αvβ3 | Multiple solid tumors | Neoangiogenic marker overexpressed on tumor vasculature and some cancer cells; dual FAP-RGD heterodimerism under study | Preclinical to phase I | Potential combination with FAP targeting | Largely preclinical; no approved indication |
| PSMA (non-prostate) | Renal cell carcinoma, glioma, triple-negative breast cancer | PSMA expressed on neoangiogenic endothelium of non-prostate solid tumors | Exploratory; no approved RLT indication | Broadens PSMA theranostic utility | Evidence largely diagnostic; therapeutic proof-of-concept limited |
Therapeutic Isotopes and Radiochemistry
Table 2. Major Therapeutic Radionuclides by Emission Type, Clinical Use, Advantages, and Constraints
| Radionuclide | Emission Type | Physical Half-Life | Tissue Range | Approved Clinical Use | Key Advantages | Key Constraints |
|---|---|---|---|---|---|---|
| Lutetium-177 (177Lu) | Beta (β−); low-energy gamma (imaging) | ~6.7 days | ~1–2 mm | mCRPC (Pluvicto); GEP-NETs (Lutathera) | Favorable dosimetry; co-emitted gamma enables SPECT imaging; established supply chain | Cross-fire limits efficacy in small-volume/micrometastatic disease |
| Actinium-225 (225Ac) | Alpha (α); yields 4 alpha particles per decay chain | ~10 days | ~47–85 μm per particle | Investigational; compassionate use in mCRPC | High linear energy transfer (LET); complex DNA damage; effective in micrometastases; active after 177Lu failure | Xerostomia from salivary PSMA exposure; supply constraints; no randomized trial completion retrieved |
| Radium-223 (223Ra) | Alpha (α) | ~11.4 days | ~<100 μm | Bone-metastatic mCRPC (Xofigo; ALSYMPCA) | Bone-selective via hydroxyapatite mimicry; OS benefit in bone-dominant mCRPC; low myelosuppression vs placebo | No ligand conjugation; restricted to bone-only disease; not a theranostic pair |
| Iodine-131 (131I) | Beta (β−); gamma | ~8 days | ~2 mm | Differentiated thyroid carcinoma; investigational PSMA-targeted | Long clinical history; established infrastructure | Thyroid toxicity; iodine trapping limits non-thyroid use; radiation precautions |
| Terbium-161 (161Tb) | Beta (β−); Auger electrons; conversion electrons | ~6.9 days | Short (Auger: nm–μm) | Early clinical (VIOLET trial in prostate cancer) | Enhanced subcellular dose deposition vs 177Lu; potentially improved micrometastatic control | Limited production capacity; supply chains immature |
| Lead-212 (212Pb) | Beta (β−) / daughter alpha (212Bi, 212Po) | ~10.6 hours | Alpha: short range | Preclinical–phase I (PSMA, SSTR, CD20 targets) | Alpha in final decay; can be used in generator systems | Very short half-life constrains logistics; supply limited |
| Copper-67 (67Cu) | Beta (β−); gamma | ~2.6 days | ~2 mm | Investigational; limited programs in dataset | Theranostic partner with 64Cu; broad chelation chemistry | Limited clinical data retrieved; cyclotron production |
Clinical Pipeline and Approved Products
Table 3. Representative Approved and Pipeline RLT Agents
| Agent | Target | Isotope | Indication | Phase / Status | Key Clinical Notes |
|---|---|---|---|---|---|
| 177Lu-PSMA-617 (Pluvicto) | PSMA | 177Lu | mCRPC post-ARPI and taxane | Approved (FDA 2022, EMA 2022) | VISION: OS 15.3 vs 11.3 months (HR 0.62); rPFS 8.7 vs 3.4 months (HR 0.40) |
| 177Lu-PSMA-617 (Pluvicto) | PSMA | 177Lu | mCRPC post-ARPI, taxane-naïve | FDA expanded indication (March 2025) | PSMAfore: rPFS 9.3 vs 5.6 months (HR 0.41; p<0.0001); OS non-significant |
| 177Lu-PSMA-617 (Pluvicto) | PSMA | 177Lu | mHSPC + ARPI + ADT | Phase III (PSMAddition) | Interim rPFS primary endpoint met; OS trend positive; numerical data not yet fully published |
| 177Lu-DOTATATE (Lutathera) | SSTR2 | 177Lu | Progressive G1–G2 midgut GEP-NETs | Approved (FDA, EMA) | NETTER-1: PFS 28.4 vs 8.4 months; ORR 18% vs 3%; OS 48.0 vs 36.3 months (not statistically significant, confounded by crossover) |
| 177Lu-DOTATATE (Lutathera) | SSTR2 | 177Lu | First-line advanced G2–G3 GEP-NETs | Phase III (NETTER-2) | PFS 22.8 vs 8.5 months; ~72% relative risk reduction; OS follow-up ongoing |
| Radium-223 dichloride (Xofigo) | Bone microenvironment | 223Ra | Bone-metastatic mCRPC | Approved (FDA, EMA); ALSYMPCA | OS 14.9 vs 11.3 months (HR 0.70); low myelosuppression; bone-only; no theranostic pair |
| 177Lu-PNT2002 (SPLASH) | PSMA | 177Lu | mCRPC post-ARPI, taxane-naïve | Phase III | rPFS 9.5 vs 6.0 months (HR 0.71); grade ≥3 TEAEs lower than control; high crossover limits OS |
| 177Lu-PSMA-I&T (ECLIPSE) | PSMA | 177Lu | mCRPC post-ARPI | Phase III | Primary rPFS endpoint met; numerical data not fully published in retrieved materials |
| 177Lu-edotreotide (ITM-11) | SSTR2 | 177Lu | Metastatic pancreatic NETs | Phase III (USA); Phase I (China) | Next-generation SSTR2 program; China/US dual-stage development |
| 225Ac-PSMA-617 (FPI-2265) | PSMA | 225Ac | mCRPC | Phase III | Key late-stage alpha-emitter PSMA program; xerostomia dose-limiting; AstraZeneca/RadioMedix |
| 225Ac-J591 (rosopatamab tetraxetan) | PSMA | 225Ac | mCRPC | Phase II | Antibody-based alpha emitter; activity in beta-refractory disease |
| 177Lu-PSMA-617 + enzalutamide (ENZA-p) | PSMA + AR | 177Lu | mCRPC | Published phase II | PSA-PFS 13.0 vs 7.8 months (HR 0.43); OS 34 vs 26 months (HR 0.55); combination rationale confirmed |
| 161Tb-PSMA-I&T (VIOLET) | PSMA | 161Tb | mCRPC | Phase I/II | PSA50 70%; median PSA-PFS 9 months; favorable tolerability; next-generation beta isotope |
| 177Lu-FAP-2286 (LuMIERE) | FAP | 177Lu | Advanced solid tumors | Phase I/II | Prolonged tumor retention; acceptable early safety; exploratory efficacy across histologies |
| 177Lu-ATL-101 (TLX591/J591) | PSMA | 177Lu | mCRPC | Phase III | Antibody-based PSMA RLT; Telix/Abzena |
| [177Lu]Lu-NeoB | GRPR | 177Lu | Prostate cancer | Phase III | Most advanced non-PSMA theranostic pipeline candidate |
Narrative: Established Practice, Clinical Trends, and Safety
PSMA-Directed RLT in Prostate Cancer
The VISION trial established 177Lu-PSMA-617 (Pluvicto) as a practice-changing option in PSMA-positive mCRPC after androgen receptor pathway inhibitor (ARPI) therapy and one to two lines of taxane chemotherapy, demonstrating a 4-month overall survival (OS) advantage and more than doubling of radiographic progression-free survival (rPFS) over standard of care 2227. The March 2025 FDA indication expansion, supported by PSMAfore data (rPFS HR 0.41; 9.3 vs 5.6 months), moved PSMA-RLT earlier—into ARPI-progressing, taxane-naïve mCRPC—allowing patients to delay or defer cytotoxic chemotherapy 1. PSMAddition signals a further shift into hormone-sensitive metastatic disease, though full numerical data await publication 2227.
Safety across PSMA-RLT programs is manageable but requires active surveillance. Grade 3 or higher hematologic toxicities—particularly anemia, thrombocytopenia, and lymphopenia—occur in a meaningful minority of patients and mirror the marrow-active nature of systemic radionuclide therapy. Xerostomia, driven by PSMA expression in salivary glands, is the signature non-hematologic adverse event; it is more prominent with alpha emitters such as 225Ac-PSMA-617, where glandular alpha dose is concentrated and potentially irreversible 25. Nephrotoxicity requires monitoring and renal-sparing strategies 12.
SSTR2-Directed RLT in Neuroendocrine Tumors
Lutathera (lutetium-177 oxodotreotide / 177Lu-DOTATATE) remains the established standard for progressive, SSTR-positive G1–G2 midgut GEP-NETs, with NETTER-1 demonstrating a PFS benefit of 28.4 versus 8.4 months and ORR improvement from 3% to 18% 346. First-line extension is now supported by NETTER-2, which reported a PFS of 22.8 versus 8.5 months in advanced G2–G3 disease, approximately a 72% relative risk reduction in progression or death, with no new safety signals versus the established profile 46. Amino acid co-infusion for nephroprotection is standard practice, and renal toxicity monitoring is integral to treatment planning 3.
Future Opportunities and Challenges
Opportunities
The clearest near-term opportunity is earlier-line PSMA-RLT in prostate cancer. The convergence of PSMAfore, SPLASH, and ECLIPSE data supports class-wide movement into taxane-naïve mCRPC, while PSMAddition may eventually open the hormone-sensitive setting 2227. Alpha-emitter RLT represents the most dynamic innovation front: 225Ac-PSMA programs (FPI-2265 in phase III) and 212Pb-based constructs offer superior potency per decay, particularly for micrometastatic disease and patients refractory to beta-emitter therapy 81825. Terbium-161, combining beta emission with Auger electrons, demonstrated a PSA50 response rate of 70% and favorable tolerability in early prostate cancer experience, suggesting next-generation isotope substitution may enhance subcellular dosimetry without major toxicity trade-offs 2728.
Combination strategies are gaining trial-level evidence: ENZA-p demonstrated that 177Lu-PSMA-617 combined with enzalutamide improved PSA-PFS (13.0 vs 7.8 months) and OS (34 vs 26 months) versus enzalutamide alone in mCRPC, validating synergy between androgen receptor pathway inhibition and PSMA-RLT 27. Pan-tumor targets, especially FAP, may redefine the reach of RLT across solid tumors beyond prostate cancer and NETs; early-phase FAP programs report disease control across sarcoma, thyroid, breast, and other histologies, with stromal remodeling potentially enhancing co-administered immune and cytotoxic therapies 24. DLL3-directed RLT in SCLC and neuroendocrine prostate cancer represents a high-priority preclinical-to-translational frontier, with 225Ac-DLL3 constructs and paired theranostic platforms entering early translational study 46.
Challenges
Isotope supply and logistics remain the most structural barrier to global scaling. Lutetium-177 production capacity has grown substantially, but actinium-225, terbium-161, and lead-212 supply chains are immature, with production bottlenecks that constrain clinical access and trial enrollment 8. Workforce and infrastructure: nuclear medicine facilities capable of administering, monitoring, and safely disposing of therapeutic radiopharmaceuticals are unevenly distributed globally, limiting equitable access 8. Patient selection complexity is growing: PSMA heterogeneity across lesions and over time, PSMA-negative escape, and the need for multi-tracer imaging (PSMA-PET plus FDG-PET or FAP-PET) to phenotype tumor biology add logistical and interpretive burdens to routine practice 1720. Dosimetry-guided personalization remains an evidence gap: individualized dosimetry is technically feasible but lacks validated prospective evidence to inform dose adjustment decisions reliably 9. Regulatory harmonization: China's National Medical Products Administration (NMPA) has accelerated reform—implementing breakthrough therapy, priority review, and conditional approval pathways for radiopharmaceuticals, and launching the 2021–2035 Medical Isotope Development Plan to achieve domestic isotope security—but global regulatory frameworks for novel isotopes, vectors, and combinations remain fragmented 26.
2026 Outlook for Clinical Practice and Research
Radioligand therapy has achieved a clinical foothold that was unimaginable a decade ago. Two approved target-isotope platforms—PSMA-177Lu and SSTR2-177Lu—are moving earlier in treatment algorithms, supported by consistent randomized data. A competitive multi-agent PSMA landscape (Pluvicto, PNT2002, ATL-101, ECLIPSE agents) is emerging, suggesting that the field is evolving beyond a single-product market toward a class of therapeutics with differentiated isotopes, ligand scaffolds, and delivery schedules 2122. Alpha-emitter programs with 225Ac and 212Pb are the most clinically actionable innovation vectors, offering a complementary mechanism after beta-emitter failure and potentially superior potency in micrometastatic disease. FAP-RLT, if early-phase signals translate to randomized evidence, could extend theranostics to nearly all solid tumor histologies. DLL3 and GRPR targets address high unmet needs in SCLC, neuroendocrine cancers, and PSMA-low prostate cancer populations.
For practicing oncologists and nuclear medicine physicians, the priority actions in 2026 are: ensuring access to validated companion PSMA or SSTR imaging before RLT initiation, integrating multidisciplinary theranostic tumor boards, monitoring hematologic and renal function throughout treatment cycles, and actively considering PSMA-RLT in taxane-naïve as well as post-taxane mCRPC settings. Awareness of emerging alpha-emitter options and participation in clinical trials investigating earlier-line use, combination strategies, and novel targets will be essential to advancing the field and offering patients the full benefit of this rapidly maturing precision oncology platform 191627.