HYNIC-TOC
A technetium-99m octreotide scan agent for neuroendocrine tumours, sold in Europe as the Tektrotyd kit
HYNIC-TOC is a version of the hormone drug octreotide with a small chemical handle that holds radioactive technetium-99m, the isotope used in most hospital gamma-camera scans. It sticks to somatostatin receptors, which most neuroendocrine tumours carry, so the scan shows where those tumours are. A kit for preparing it, Tektrotyd, is authorised in Poland and, since 2016, in many other European countries; it is not approved in the United States. It is used only in nuclear medicine departments.
Manufacturer's recommended dosing (European national label): 370-740 MBq of technetium-99m HYNIC-TOC, Single injection, Intravenous Details ↓
Recommended Dosing
Manufacturer's recommended dosing (European national label)
From the prescribing information. Other doses studied, if any, are in the full dosing data below.
Used in human trials
No manufacturer dose exists for this use: these are amounts given in published trials, not recommendations.
What is it?
Radioligand imaging works by attaching a radioactive atom to a molecule that seeks one target in the body. After injection the molecule collects where its target is, and a camera outside the body records the radiation. HYNIC-TOC does this for somatostatin receptors, which are carried in large numbers by most neuroendocrine tumours, the slow-growing cancers that arise from hormone-making cells in the gut, pancreas and lungs. The camera here is a gamma camera, used for planar images or for SPECT, its three-dimensional form, often fused with a CT scan.
The targeting part is Tyr3-octreotide, a close relative of octreotide, the long-used somatostatin drug. A hydrazinonicotinyl (HYNIC) group is attached to hold technetium-99m, and a second small molecule, EDDA, completes the complex. Technetium-99m is the most widely used isotope in nuclear medicine. The older standard, indium-111 pentetreotide (Octreoscan), has drawbacks its developers listed plainly: limited availability, gamma energy poorly suited to imaging and a higher radiation dose, and it is usually imaged again a day after injection. The first ten patients scanned with HYNIC-TOC in Innsbruck in 2000 showed tumours within 15 minutes, with sharper contrast and more lesions seen than with indium-111 tracers.
In a 2003 Austrian comparison of 41 patients scanned both ways, HYNIC-TOC agreed with indium-111 octreotide in 78% and was more sensitive overall, with two false positives from bowel activity that early extra images can avoid. Its average effective dose in a 28-patient dosimetry study was 4.6 mSv, and a 2016 Swedish assessment report put it at about 3.8 mSv for a 740 MBq injection. Children absorbed about 30% more per megabecquerel than adults in a separate study.
It has been studied well beyond gut tumours. It localised the small tumours that cause tumour-induced osteomalacia in 69 of 80 patients with 99% specificity, beat iodine-131 MIBG for paragangliomas outside the adrenal gland (96% against 72%), found medullary thyroid cancer in about four of five patients with raised calcitonin, and separated cancerous from benign lung nodules. Researchers have even used it to measure inflammation after a heart attack. Long-acting octreotide treatment did not stop tumours taking it up in two studies, though it lowered uptake in normal liver and spleen, so patients do not necessarily need to pause their medicine before the scan.
Its limits are those of single-photon imaging. Gallium-68 somatostatin PET (DOTATATE, DOTATOC or DOTANOC) is more sensitive and has become the standard where it is available; in 173 Romanian patients with gut and pancreatic tumours HYNIC-TOC SPECT/CT reached 90.5% sensitivity, which the authors noted was below published gallium-68 figures. SPECT/CT added clear value over planar images alone in a 65-patient series. Its advantage is access: a hospital without a PET scanner or gallium generator can still offer somatostatin receptor imaging.
Regulatory status differs by country. FDA has not approved it and the European Medicines Agency's central register holds no record, because it was authorised country by country. Poland approved the Tektrotyd kit from the Polish national radioisotope centre (POLATOM) first; in May 2016 a European decentralised procedure led by Sweden concluded, and the developer reported certificates in 19 European countries including Germany, France, Italy, Spain and the UK. The Swedish public assessment report gives an adult activity of 370 to 740 MBq for neuroendocrine tumour imaging. It is a radiopharmaceutical kit prepared in hospital; there is nothing for an individual to buy.
Mechanism of Action
HYNIC-TOC binds somatostatin receptors like octreotide and carries technetium-99m so that receptor-rich tumours show on a gamma-camera scan.
Somatostatin receptor binding
The Tyr3-octreotide part binds the same receptors as octreotide, which most neuroendocrine tumours carry in large numbers (2003 comparison).
Gamma-camera imaging
Technetium-99m, held by the HYNIC group with EDDA, emits gamma rays imaged by planar scans or SPECT/CT, usually 2 to 4 hours after injection.
Normal uptake and clearance
The spleen, kidneys and liver take up the most in normal tissue; urinary excretion was lower than with indium-111 octreotide (first clinical study, dosimetry study).
Published Research
Studies of technetium-99m HYNIC-TOC (also EDDA/HYNIC-TOC and Tektrotyd), read from their PubMed abstracts: the first clinical use, the comparison with indium-111 octreotide, dosimetry, and studies in specific tumours. Studies of other technetium octreotide variants such as HYNIC-TATE are not carded.
First clinical results
Ten cancer patients were scanned in Innsbruck. Tumours were visible within 15 minutes and contrast peaked at 4 hours; compared in the same patients, the new tracer gave higher tumour-to-background ratios and showed significantly more lesions than indium-111 DTPA-octreotide or DOTA-TOC, with lower urinary excretion.
Intrapatient comparison with Octreoscan
Forty-one patients had both scans (350-400 MBq of HYNIC-TOC, 150 MBq of indium-111 octreotide). Results matched in 78%; indium-111 was falsely negative in 6 cases and HYNIC-TOC falsely positive in 2 from bowel activity. HYNIC-TOC was judged more sensitive, with extra scans at 1-2 hours advised.
Radiation dosimetry
Patient-specific dosimetry in 28 people imaged for suspected neuroendocrine tumours gave a mean effective dose of 4.6 mSv. The spleen, kidneys and liver received the most (0.030, 0.021 and 0.012 mGy per MBq), and kidney and tumour doses varied widely between patients.
Dosimetry in children
In 11 children and teenagers, uptake patterns matched adults' but organ doses per MBq were about 30% higher (kidneys 0.024, spleen 0.032 mGy per MBq), with large variation between patients.
SPECT/CT against planar imaging
In 65 patients with proven neuroendocrine tumours given 670 MBq, SPECT/CT had 89% sensitivity and 79% specificity, and its accuracy (85%) was significantly better than planar whole-body imaging (72%); it changed treatment for 17% of patients.
173 gut and pancreatic tumours
In a retrospective Romanian series, HYNIC-TOC whole-body imaging with SPECT/CT gave 90.5% sensitivity, 71.9% specificity and 84.3% accuracy for gastroenteropancreatic neuroendocrine tumours, below published figures for gallium-68 DOTA peptides.
Long-acting octreotide does not block it
Comparing 30 patients on long-acting octreotide with 30 not on it, tumour-to-muscle ratios in primaries and metastases did not differ; uptake in normal liver and bone was lower in treated patients.
Quantified effect of somatostatin drugs
In 177 patients (55 on long-acting somatostatin analogues), the drugs cut normal organ uptake (spleen SUVmax about 13 against 34) but did not reduce uptake in most tumour sites, and bone metastases took up more.
Use in daily practice
In 117 patients across six clinical questions, the scan was most useful for staging known tumours and restaging after surgery (recurrence in 7 of 47), and less useful for confirming suspected tumours or assessing lung nodules.
Tumours causing osteomalacia
Among 183 patients with low phosphate and suspected tumour-induced osteomalacia, whole-body HYNIC-TOC imaging found the culprit tumour in 69 of 80 (86%) and correctly excluded 102 of 103 without it, for 93% overall accuracy.
Paraganglioma against MIBG
In 97 patients with suspected phaeochromocytoma and normal adrenal CT, HYNIC-TOC found 96% of tumours outside the adrenal glands against 72% for iodine-131 MIBG, but only 50% of adrenal tumours against 86%.
Medullary thyroid cancer
Forty-five patients were imaged 2 and 4 hours after 740 MBq. In those with raised calcitonin after surgery, 74% had true-positive scans; overall sensitivity was 80%, specificity 83% and positive predictive value 97%.
Solitary lung nodules
In 43 patients given 740-925 MBq, 26 of 29 malignant nodules took up the tracer, including 24 of 25 primary lung cancers, while 10 of 14 benign nodules did not.
Inflammation after heart attack
In 14 patients a week after anterior myocardial infarction, 7 showed tracer uptake in the heart. Its intensity correlated with infarct size and with heart enlargement over 6 months, suggesting a way to image post-infarct inflammation.
Pitfalls in 310 patients
A Polish review drawing on 310 scans with the Tektrotyd kit describes how labelling errors, acquisition choices and normal or inflammatory uptake can mislead readers, and notes clinical use since 2005.
Dosing Data
The first row is the adult activity for the Tektrotyd kit as authorised in Europe, from the Swedish public assessment report for the decentralised procedure; it is a European national label, not an FDA label. The other rows are the activities injected in the published human studies carded above, each a single dose before imaging.
Educational information, not medical advice. Each dose above is tagged with its source: an approved label, a published human study, animal data, or amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
What a Buyer Needs to Know
What is sold, how it is mixed, stored and taken, and what is known about its safety, quality and legal status. Each part names its source. Where we have none, it says unknown.
What is sold
Unknown: we hold no regulator's label that says in what form HYNIC-TOC is supplied. It is a radioactive drug: the next part says where it is prepared and given.
Mixing a vial: a worked example
Nothing to mix at home, and no syringe units to work out: HYNIC-TOC is a radioactive drug, prepared and given in nuclear-medicine departments, and its dose is an amount of radioactivity (MBq or GBq), not a weight.
This page's dosing note: “HYNIC-TOC is prepared from a kit with technetium-99m in a hospital radiopharmacy and dosed by radioactivity; no reconstitution maths applies.”
Source: this page's own note in Dosing Data below; the amount of each dose row in Dosing Data below.
Storage before and after mixing
Unknown: no label on file says how HYNIC-TOC is stored. It is a radioactive drug held by the nuclear-medicine department that prepares and gives it (see the part above); the home rules for a mixed vial in the mixing guide do not apply to it.
How it is taken
As the approved label gives it: Intravenous (Single injection; Tektrotyd kit, adults with neuroendocrine tumours (European label)).
Source: Manufacturer's recommended dosing (European national label): the route and frequency of each row in Dosing Data below.
What to expect, and when
How long it stays in the body: not established by a measurement cited on this entry.
How long the doses were given: Tektrotyd kit, adults with neuroendocrine tumours (European label): One scan.
When effects appear: unknown; no source on this page gives a time to effect for HYNIC-TOC. Results reported in the studies are under Published Research.
Source: Manufacturer's recommended dosing (European national label), the duration of each row in Dosing Data below.
Side effects, and when to stop or get help
From the Side Effects section: Brief headache or upper abdominal pain just after injection; Radiation exposure: about 4.6 mSv per scan in a 28-patient dosimetry study, about 30% more per MBq in children. Full list and cautions ↓
When to stop or get help: unknown; no label or trial on file sets rules for stopping HYNIC-TOC. Treat a severe or unexpected reaction as a reason to stop and see a doctor.
Source: the Side Effects section below (“The abstracts above report no adverse reactions to the tracer”).
Interactions
Unknown: a PubMed search for human interaction studies of HYNIC-TOC (reviewed 2026-10-28) found none. Unknown is not the same as safe to combine.
Every peptide's record, with its source: the interaction matrix.
Checking what you bought
Unknown: no published independent test of HYNIC-TOC products is in our lab-results database yet, so how products sold under this name measure up is not known.
To read a certificate of analysis, paste it into the COA decoder; it checks the measured mass against HYNIC-TOC's expected mass, 1,170.4 Da, from this entry's molecular data. Trust & Verification explains what independent testing can and cannot show.
Legal status
US: Not FDA Approved (Not approved by FDA (no Drugs@FDA record, openFDA, searched October 29, 2026) and not in the EMA's central medicines list). Elsewhere: approved in European countries (Tektrotyd kit; decentralised procedure SE/H/1509/01/DC concluded May 24, 2016; Poland earlier). Sport: Unsettled (S0 may apply).
Country by country ↓ · Regulatory tracker
Source: this entry's approval status and the WADA Prohibited List, as in Legal Status below.
Side Effects & Contraindications
Reported Side Effects
The abstracts above report no adverse reactions to the tracer. From the Swedish public assessment report for Tektrotyd (2016):
Contraindications & Cautions
Points from the Swedish assessment report and the studies above:
Legal Status
HYNIC-TOC is authorised nationally in many European countries as the Tektrotyd kit and is not approved in the United States.
Frequently Asked Questions
?What is a HYNIC-TOC scan?
A somatostatin receptor scan using a technetium-99m version of octreotide. After the injection, a gamma camera shows where tumours with these receptors, mostly neuroendocrine tumours, have taken it up.
?Is it approved?
In Europe, yes, country by country: the Tektrotyd kit went through a decentralised procedure in 2016 and is authorised in Poland and many other countries. It is not approved by FDA.
?How does it compare with gallium-68 dotatate PET?
Gallium-68 PET is more sensitive and is the standard where available. HYNIC-TOC uses the technetium-99m most hospitals already have, so it is an option where PET or a gallium generator is not.
?Do I need to stop octreotide before the scan?
That decision belongs to the treating team. Two studies found long-acting octreotide did not reduce tumour uptake of HYNIC-TOC, though it lowered uptake in normal organs.
?Can I buy it?
No. It is a radiopharmaceutical kit labelled with technetium-99m in a hospital radiopharmacy and injected by nuclear medicine staff.
References
- [other] PubChem CID 137331866 (synonyms HYNIC-TOC, hydrazinonicotinyl-Tyr3-octreotide): formula C55H71N13O12S2, molecular weight 1170.4. Read October 28, 2026. https://pubchem.ncbi.nlm.nih.gov/compound/137331866
- [registry] ClinicalTrials.gov API v2, read October 28, 2026: NCT02691078 (phase 2, validation of 99mTc-EDDA-HYNIC-TOC kits, completed).
- [other] Swedish Medical Products Agency, Public Assessment Report: Tektrotyd kit for radiopharmaceutical preparation, decentralised procedure SE/H/1509/01/DC, finalised May 24, 2016 (adults: 370-740 MBq; effective dose about 3.8 mSv after 740 MBq). Read October 29, 2026.
- [other] National Centre for Nuclear Research (NCBJ), 'Tektrotyd, a new medicine from Poland, registered in Europe', June 9, 2016: certificates of registration in 19 European countries; earlier admitted to the Polish market. Read October 29, 2026.
- [other] US FDA, Drugs@FDA (openFDA): no application for HYNIC-TOC or Tektrotyd. Searched October 29, 2026.
- [pubmed] Decristoforo C, et al. "99mTc-EDDA/HYNIC-TOC: a new 99mTc-labelled radiopharmaceutical for imaging somatostatin receptor-positive tumours; first clinical results and intra-patient comparison with 111In-labelled octreotide derivatives." Eur J Nucl Med, 2000;27(9):1318-25. PMID: 11007513.
- [pubmed] Gabriel M, et al. "An intrapatient comparison of 99mTc-EDDA/HYNIC-TOC with 111In-DTPA-octreotide for diagnosis of somatostatin receptor-expressing tumors." J Nucl Med, 2003;44(5):708-16. PMID: 12732671.
- [pubmed] Grimes J, et al. "Patient-specific radiation dosimetry of 99mTc-HYNIC-Tyr3-octreotide in neuroendocrine tumors." J Nucl Med, 2011;52(9):1474-81. PMID: 21795364.
- [pubmed] Hou X, et al. "Patient-specific dosimetry of (99m)Tc-HYNIC-Tyr(3)-Octreotide in children." EJNMMI Phys, 2017;4(1):24. PMID: 29030760.
- [pubmed] Trogrlic M, et al. "Incremental value of (99m)Tc-HYNIC-TOC SPECT/CT over whole-body planar scintigraphy and SPECT in patients with neuroendocrine tumours." Nuklearmedizin, 2017;56(3):97-107. PMID: 28164207.
- [pubmed] Gherghe M, et al. "The New Radiolabeled Peptide (99m)TcEDDA/HYNIC-TOC: Is It a Feasible Choice for Diagnosing Gastroenteropancreatic NETs?" Cancers (Basel), 2022;14(11). PMID: 35681704.
- [pubmed] Li Y, et al. "Long-acting octreotide treatment has no impact on tumor uptake of 99mTc-HYNIC-TOC in patients with neuroendocrine tumors." Nucl Med Commun, 2019;40(10):1005-1010. PMID: 31365494.
- [pubmed] Gemmell AJ, et al. "Quantitative uptake in 99m Tc-EDDA/HYNIC-TOC somatostatin receptor imaging - the effect of long-acting release somatostatin analogue therapy." Nucl Med Commun, 2023;44(11):944-952. PMID: 37578312.
- [pubmed] Chrapko BE, et al. "99mTc-EDDA/HYNIC-TOC somatostatin receptor scintigraphy in daily clinical practice." Med Sci Monit, 2010;16(4):MT35-44. PMID: 20357727.
- [pubmed] Jing H, et al. "Effective detection of the tumors causing osteomalacia using [Tc-99m]-HYNIC-octreotide (99mTc-HYNIC-TOC) whole body scan." Eur J Radiol, 2013;82(11):2028-34. PMID: 23721625.
- [pubmed] Chen L, et al. "99mTc-HYNIC-TOC scintigraphy is superior to 131I-MIBG imaging in the evaluation of extraadrenal pheochromocytoma." J Nucl Med, 2009;50(3):397-400. PMID: 19223405.
- [pubmed] Czepczyński R, et al. "Somatostatin receptor scintigraphy using 99mTc-EDDA/HYNIC-TOC in patients with medullary thyroid carcinoma." Eur J Nucl Med Mol Imaging, 2007;34(10):1635-45. PMID: 17530247.
- [clinical-trial] Płachcińska A, et al. "99mTc-EDDA/HYNIC-TOC scintigraphy in the differential diagnosis of solitary pulmonary nodules." Eur J Nucl Med Mol Imaging, 2004;31(7):1005-10. PMID: 15029463.
- [pubmed] Sazonova SI, et al. "Potential utility of SPECT/CT with 99mTc-Tektrotyd for imaging of post-myocardial infarction inflammation." J Nucl Cardiol, 2023;30(6):2544-2555. PMID: 37316747.
- [review] Garai I, et al. "Limitations and pitfalls of 99mTc-EDDA/HYNIC-TOC (Tektrotyd) scintigraphy." Nucl Med Rev Cent East Eur, 2016;19(2):93-8. PMID: 27479887.
Sources & Citations
Studies were read from their PubMed abstracts on October 29, 2026; regulatory status from the Swedish Medical Products Agency public assessment report for Tektrotyd, the NCBJ announcement of June 9, 2016, Drugs@FDA (openFDA) and the EMA medicines list, read October 28-29, 2026. The formula is PubChem's.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.