# Antigen

Source: https://onco.cc/terms/antigen/  
OnCo record `antigen` (Term). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Anything an antibody or immune cell can recognise, typically a protein on a cell's surface. In cancer, an antigen is the flag that tells a drug or an immune cell 'this is the cell to attack'.

## Summary

Most cancer antigens are ordinary human proteins that a tumour makes in unusual amounts (HER2, TROP2, CD19, PSMA), so drugs targeting them also touch normal cells that carry a little; truly tumour-specific antigens arise from mutations (neoantigens) or from viral proteins. A good drug antigen is abundant on tumour cells, scarce on essential normal tissue, and stable over time. Tumours escape by losing the antigen, which is how CD19-negative relapse defeats CAR-T, and by hiding the pieces of antigen they would normally display to T cells.

## Fields

- Kind: Term
- Last checked: 2026-09-09
- Also known as: antigens; tumour antigen; tumour antigens; tumor antigen; tumor antigens; target antigen; target antigens; antigenic; tumour-associated antigen; tumour-associated antigens; tumor-associated antigen; tumor-associated antigens; antigen-negative; antigen loss

## Sources

- Wikipedia: https://en.wikipedia.org/wiki/Antigen
- Wikipedia: https://en.wikipedia.org/wiki/Antigen

## Connected records

- terms: [Antibody](https://onco.cc/terms/antibody/), [Drug resistance (primary and acquired)](https://onco.cc/terms/resistance/), [Epitope](https://onco.cc/terms/epitope/), [Immune system](https://onco.cc/terms/immune-system/), [Monoclonal](https://onco.cc/terms/monoclonal/), [Neoantigen](https://onco.cc/terms/neoantigen/), [T cell](https://onco.cc/terms/t-cell/)
- pathways: [Antigen presentation & immune editing](https://onco.cc/pathways/antigen-presentation-immunoediting/)
- technologies: [Antibody-drug conjugate (ADC)](https://onco.cc/technologies/adc/), [CAR-T cell therapy](https://onco.cc/technologies/car-t/), [T-cell engagers (bispecific)](https://onco.cc/technologies/t-cell-engager/)
- targets: [BCMA](https://onco.cc/targets/bcma/), [CD19](https://onco.cc/targets/cd19/), [HER2](https://onco.cc/targets/her2/), [PSMA](https://onco.cc/targets/psma/), [TROP2](https://onco.cc/targets/trop2/)

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JSON: https://onco.cc/api/v1/entities/antigen.json