The American Association for Cancer Research is the world's biggest oncology meeting. Its 2026 edition, running this week in San Diego, has a theme nobody scheduled on purpose: peptides are at the center of the new cancer drug classes landing there. Not one program, but at least four, from at least six companies, across three different mechanisms. Here is a map.

Targeted radiation

Radioligand therapy works by attaching a radioactive atom to a molecule that finds a specific marker on tumor cells. The drug travels through the body, sticks to the tumor, and the radiation kills only the cells it sticks to. Two approved drugs in this class (Pluvicto for prostate cancer, Lutathera for neuroendocrine tumors) together generated $2.7 billion in sales last year. Both use peptide-based targeting molecules. The radioligand market is projected to reach $10.9 billion by 2035 ↗.

At AACR this week, AlphaGen presented two new radioligands ↗ that use a different kind of radiation called alpha particles. Alpha particles travel only a few cell-widths in tissue, so the radiation damage stays tightly concentrated on the tumor cells the peptide binds, with less collateral damage to nearby healthy tissue. Both programs showed tumor growth inhibition in animal studies. One of them, targeting a protein called FAP that shows up across many solid tumors, has already moved into patient imaging.

Hitting targets inside the cell

Most cancer drugs can only see proteins on the outside of tumor cells. But most cancer-driving proteins are inside the cell, out of reach of conventional drugs.

A newer approach gets around this. When a cell processes an internal protein, short peptide fragments from it get displayed on the cell surface, attached to a presentation molecule called MHC. A drug that recognizes that specific peptide-MHC combination can address the entire internal protein landscape as a target space.

Deck Bio unveiled DBXO-1 at AACR this week ↗, a drug that recognizes several peptide-MHC combinations at once, rather than just one (which is how the first approved drug in this class, tebentafusp, worked). In preclinical models, the drug binds its targets at 1-2 nanomolar (a very strong binding affinity) with more than 1,000-fold preference for targeted versus non-targeted cells. The target population across lung and gastroesophageal cancers is about 120,000 people in the U.S., Europe, U.K., and Australia.

Macrocyclic peptides: the middle-space drug class

Macrocyclic peptides are peptide rings, chemically modified to resist breakdown in the body. They sit in a space between small-molecule pills (which cannot handle large, flat drug targets) and injectable antibodies (which cannot be taken as pills). Macrocycles can sometimes do both jobs.

Several AACR presenters are working this space in oncology. Circle Pharma's CID-078 debuted at a clinical plenary. Bicycle Therapeutics presented head-and-neck cancer data showing 40% of treated patients responded to their peptide-drug conjugate BT5528.

The money is following. Syneron Bio closed a $150M Series B in March ↗ with Abu Dhabi's sovereign wealth fund and Singapore's Temasek backing an AI-driven macrocyclic peptide platform. AstraZeneca was already in. Its March 2025 deal with Syneron was $75M upfront and up to $3.4 billion in milestones. A separate Biogen-Dayra deal from late 2025 ↗ put another $50M upfront on oral macrocyclic peptides for immune conditions.

Why this matters

For most of the last twenty years, the main oncology drug classes have been small-molecule pills (kinase inhibitors) and biologic antibodies (drugs like Keytruda and Opdivo). Peptides have been a sidekick modality. AACR 2026 is the clearest sign yet that they are becoming a main character, across mechanisms that each fix a different limitation of the older classes. Radioligands concentrate radiation on tumor cells with less collateral damage. Peptide-MHC engagers can reach targets inside the cell where most cancer biology happens. Macrocycles get close to antibody-like behavior in a pill.

None of these drug classes is brand new. What is new is how many of them arrived at the same meeting with real data in the same week, and how much capital is behind all of them.

What we host

Our platform catalogs peptide candidates against the major oncology target families, including the somatostatin receptors used by Lutathera and AlphaGen's AG1002 program, the FAP target in AlphaGen's AG1206, and the macrocyclic scaffolds that underpin the drugs coming out of Bicycle, Circle, and Syneron. The card-level design questions at stake (binding affinity, stability, selectivity, delivery route) are the same questions every company above is answering one molecule at a time.