OncoFirm™ / Research / Human cancer antigens

Research explainer · Glycobiology

Peanut Agglutinin (PNA) in Cancer Detection: How a Plant Lectin Reveals the Thomsen–Friedenreich Antigen

Cancer changes the sugars on a cell’s surface. One of the best-studied changes is the exposure of the Thomsen–Friedenreich (TF) antigen, a small two-sugar structure that healthy cells usually keep hidden. Peanut agglutinin (PNA), a protein from peanuts that binds this sugar, has been used for decades to find it. This guide explains how PNA works, where it is used, what it cannot do, and how TF-antigen research is moving from tissue slides toward blood tests.

By OncoFirm™ Scientific TeamPublished 11 Aug 2025Updated 1 Oct 2026Sources peer-reviewed, linked

At a glance

What PNA is

A sugar-binding protein (lectin) from peanuts, Arachis hypogaea

What it binds

Galβ1-3GalNAc, the Thomsen–Friedenreich (TF) antigen, also called T antigen or CD176

Where it is used

Tissue research staining, blood-bank red-cell testing, glycan capture assays

Main caution

A research tool: binding is not specific to one cancer and is not a diagnosis

OncoFirm™ status

TF / Gal-GalNAc test concepts in development; not FDA cleared or approved

On this page

Key points

PNA and the TF antigen in brief

~90%of carcinomas showed T or Tn antigen exposure in Springer's landmark 1984 review
2 sugarsGal-β1,3-GalNAc, the TF disaccharide that PNA binds once its sialic acid cap is lost
Up to 5 µg/mLPNA measured in volunteers' blood about an hour after eating 200 g of peanuts (2014 study)

Figures are from the peer-reviewed studies listed in the references.

Definition

What is peanut agglutinin?

Peanut agglutinin (PNA) is a lectin, a protein that recognizes specific sugars, purified from peanuts (Arachis hypogaea). It is built from four identical subunits and binds most strongly to galactose-β1,3-N-acetylgalactosamine (Galβ1-3GalNAc), the core sugar of the Thomsen–Friedenreich antigen.

Lectins like PNA are workhorses of glycobiology because they read sugar structures that antibodies often struggle with. PNA is inexpensive, stable and easy to label with fluorescent dyes, enzymes or biotin, which is why it became a standard tool for studying the Thomsen–Friedenreich (TF) antigen in tissue.

How it works

How PNA finds the Thomsen–Friedenreich antigen

How peanut agglutinin detects the Thomsen–Friedenreich antigenOn a normal cell, the Thomsen–Friedenreich disaccharide (galactose linked to N-acetylgalactosamine on a protein) is usually capped by sialic acid, which blocks peanut agglutinin from binding. On many cancer cells the cap is missing, so the disaccharide is exposed and peanut agglutinin, a four-part lectin, binds it. A label on the lectin then reveals the binding as a tissue stain, red-cell agglutination or a signal in a capture assay.NORMAL CELLSialic acid cap hides TF: PNA cannot bindMANY CANCER CELLSCap missing, TF exposed: PNA bindsLABELLED PNA REVEALS ITTissue stainingfluorescent or enzyme labelRed-cell testingT-activation in blood banksCapture assaysTF-bearing glycoproteinsGalNAcGalactoseSialic acidPNA (tetramer)TF antigen = Galβ1-3GalNAc · symbols follow SNFG

On healthy cells the TF disaccharide is usually capped by sialic acid or built into longer chains, which blocks PNA. When cancer disrupts glycosylation, TF is left exposed and labelled PNA binds it.

  1. Normal glycosylation. Proteins such as the mucin MUC1 carry O-linked sugar chains. The TF core is normally extended or capped with sialic acid.
  2. Cancer-associated change. Altered enzyme activity in many tumors truncates these chains, exposing TF (and its precursor, Tn) on the cell surface and on shed glycoproteins.
  3. Lectin binding. PNA recognizes the exposed Galβ1-3GalNAc. Sialylated TF is largely invisible to it.
  4. Readout. A label on PNA, fluorescent or enzymatic, turns binding into a visible stain or a measurable signal.

For the causes of TF exposure, see what causes high Thomsen–Friedenreich antigen and the mucin carrier MUC1.

Where PNA is used

Three established uses, and one research direction

  • Tissue histochemistry (research). Labelled PNA has been applied to sections of colon, breast, bladder, stomach and other tissues to map TF exposure. Studies link stronger TF expression with tumor progression in several cancers, but staining patterns vary and PNA also binds some normal tissues.
  • Transfusion medicine. Blood banks use PNA, alongside other lectins, to recognize T-activated red cells, where bacterial enzymes have stripped sialic acid and exposed T antigen. It is a good example of PNA giving a reliable, practical answer when the question is narrow.
  • Glycoprotein capture. In research assays, PNA can capture TF-bearing glycoproteins from serum or cell extracts, often paired with an antibody to a specific protein such as MUC1.
  • Related chemistry for screening. The galactose oxidase–Schiff (GOS) reaction detects the same Gal-GalNAc structure chemically and has been studied as a rapid screen on rectal mucus for colorectal cancer. It shows the long-standing interest in Gal-GalNAc as a simple, low-cost marker.

Why TF matters

TF is more than a passive marker

Research from the University of Liverpool has shown that exposed TF on cancer-associated MUC1 can take part in metastasis. Galectin-3, a sugar-binding protein that rises in the blood of many patients with metastatic cancer, binds TF on MUC1 and increased the adhesion of breast and colon cancer cells to blood-vessel lining in laboratory experiments.

The same group found that some dietary PNA survives digestion: up to 5 µg/mL was measured in volunteers’ blood about an hour after eating 200 g of peanuts. In laboratory models this circulating PNA mimicked galectin-3, and a 2021 follow-up reported that it prompted blood-vessel cells to release metastasis-promoting cytokines. These are laboratory and small human studies; they have not been shown to change cancer outcomes and are not dietary advice.

For the diagnostics field, the takeaway is that TF exposure reflects real tumor biology, which is why it remains a target worth measuring. Learn more in what are cancer biomarkers?.

Limitations

What PNA cannot tell you

  • Not cancer-specific. TF exposure occurs in many carcinomas and some leukemias, and PNA binds certain normal and inflamed tissues. A positive result does not identify the cancer or its location.
  • Sialylation hides signal. TF capped with sialic acid is largely invisible to PNA, so binding depends on how much antigen is unmasked in a given sample.
  • Variable methods. Fixation, staining protocols, lectin lots and scoring differ between studies, which makes results hard to compare.
  • Interferences in blood. Serum contains many glycoproteins and natural anti-T antibodies that can compete with or mask binding in solution assays.
  • No cleared blood test. There is no FDA-cleared blood test based on PNA or the TF antigen for cancer screening or diagnosis.

From tissue to blood

Can TF antigen be measured in a blood test?

Moving TF measurement from a tissue slide into a blood sample is an active research question. It requires capture reagents with defined specificity, whether lectins such as PNA or monoclonal antibodies against TF, a way to separate tumor-derived glycoforms from normal background, and quantitative readout so that results can be compared over time.

Multiplexing helps. Because no single glycan or protein marker is specific enough on its own, the most promising designs combine TF with established protein markers such as CEA, PSA and AFP, and interpret them together. See tumor antigen detection and AI-driven biomarkers.

OncoFirm™ research

How TF-antigen science informs OncoFirm™'s pipeline

OncoFirm™ was founded on the idea that cancer-associated antigens, including the TF and Gal-GalNAc glycans that PNA made visible in tissue, could one day be measured quickly and affordably from a drop of blood. Our work focuses on doing that responsibly: quantitatively, with clear evidence, and as part of multi-marker panels.

TF and Gal-GalNAc concepts

Named pipeline concepts that target TF and Gal-GalNAc antigens, including OncoFirm™-R, OncoFirm™-B and OncoFirm™-L.

Evidence-led capture reagents

Lectins and anti-TF antibodies evaluated side by side, with specificity tested against benign and inflammatory conditions.

Quantitative fluorescence

A self-calibrating fluorescent strip and handheld reader designed to report numbers rather than faint lines. Platform

Panels, not single markers

Research on TF alongside CEA, PSA and AFP on one strip, read in separate zones. OncoFirm™ MultiDx

See how one reader can support a growing test menu in one reader, one strip design, or explore the Cancer Biomarker Atlas 2026.

OncoFirm™ test concepts, reagents and reader are in development, have not been cleared or approved by the FDA, and are for research use only. Blood measurement of TF antigen is at an early research stage.

FAQ

Frequently asked questions

What is peanut agglutinin (PNA)?

Peanut agglutinin is a lectin, a sugar-binding protein, purified from peanuts (Arachis hypogaea). It is made of four identical subunits and binds most strongly to the disaccharide galactose-β1,3-N-acetylgalactosamine, known as the Thomsen–Friedenreich (TF or T) antigen.

Why does PNA bind to cancer cells?

Many cancer cells glycosylate their proteins abnormally. The TF disaccharide, which is normally capped by sialic acid or extended into longer sugar chains, is left exposed on the cell surface, where PNA can bind it.

Is PNA used to diagnose cancer?

Not on its own. PNA has been used for decades as a research and histochemistry tool to study TF antigen in tissue, and in blood banks to detect T-activated red cells. It is not an FDA-cleared cancer test, and PNA binding is not specific to any one cancer or organ.

Is the Thomsen–Friedenreich antigen the same as Gal-GalNAc?

Yes, in practice. The TF antigen is the Gal-β1,3-GalNAc disaccharide attached to proteins, also called the T antigen or CD176. Gal-GalNAc is a shorthand name for the same sugar structure.

Does eating peanuts affect cancer?

Laboratory and small human studies from the University of Liverpool found that some PNA survives digestion and reaches the blood, where it can bind cancer-associated MUC1 and increase cancer-cell adhesion in laboratory models. These findings have not been shown to change cancer outcomes in people, and they are not dietary advice; patients should talk to their care team.

Does OncoFirm™ have a TF antigen blood test?

Not yet. OncoFirm™ has named pipeline concepts that target TF and Gal-GalNAc antigens, and is developing a quantitative fluorescent lateral flow platform. These are in development, have not been cleared or approved by the FDA and are for research use only.

Sources

References

  1. Springer GF. T and Tn, general carcinoma autoantigens. Science. 1984;224(4654):1198–1206. doi.org/10.1126/science.6729450
  2. Yu LG. The oncofetal Thomsen–Friedenreich carbohydrate antigen in cancer progression. Glycoconjugate Journal. 2007;24:411–420. doi.org/10.1007/s10719-007-9034-3
  3. Yu LG, Andrews N, Zhao Q, et al. Galectin-3 interaction with Thomsen-Friedenreich disaccharide on cancer-associated MUC1 causes increased cancer cell endothelial adhesion. J Biol Chem. 2007;282(1):773–781. doi.org/10.1074/jbc.M606862200
  4. Zhao Q, et al. Peanut agglutinin appearance in the blood circulation after peanut ingestion mimics the action of endogenous galectin-3 to promote metastasis by interaction with cancer-associated MUC1. Carcinogenesis. 2014;35(12):2815–2821. pubmed.ncbi.nlm.nih.gov/25326505/
  5. Wang W, Sindrewicz-Goral P, Chen C, et al. Appearance of peanut agglutinin in the blood circulation after peanut ingestion promotes endothelial secretion of metastasis-promoting cytokines. Carcinogenesis. 2021;42(8):1079–1088. doi.org/10.1093/carcin/bgab059
  6. Usefulness of galactose oxidase-Schiff test in rectal mucus for screening of colorectal malignancy. Anticancer Research (PubMed 11396195). pubmed.ncbi.nlm.nih.gov/11396195/
  7. Canadian Society for Transfusion Medicine. Do you want to know more about lectins? transfusion.ca/technical/do-you-want-to-know-more-about-lectins/

About this article. Written by the OncoFirm™ Scientific Team from peer-reviewed publications and professional sources, all linked above. OncoFirm™ was not involved in the studies discussed. This article is for education and is not medical or dietary advice. OncoFirm™ assays are in development, have not been cleared or approved by the FDA and are not available for sale.

Collaborate on glycan biomarker research

Glycobiology groups, pathologists and clinical partners working on TF, Tn or MUC1 glycoforms can explore joint studies with OncoFirm™. Collaboration inquiry

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